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GASOLINE  TRACTORS 


A  PRACTICAL  PRESENTATION  OF  TRACTOR 
PROBLEMS  AND  THEIR  SOLUTION 


CHARLES  B.  HAYWARD 

PKESIDENT    AND    GENERAL    MANAGER,    THE    STIRLING    PRESS,    NEW    YOKK    CITY 
MEMBER,    SOCIETY    OF    AUTOMOBILE    ENGINEERS 

MEMBER,    THE    AERONAUTICAL    SOCIETY 

FORMERLY    SECRETARY,    SOCIETY    OF    AUTOMOBILE    ENGINEERS 
FORMERLY    ENGINEERING    EDITOR,    The    Automobile 


AMERICAN   TECHNICAL   SOCIETY 

CHICAGO 

1920 


COPYRIGHT,    1919,    BY 

AMERICAN  TECHNICAL  SOCIETY 


COPYRIGHTED    IN    GREAT    BRITAIN 
ALL   RIGHTS   RESERVED 


INTRODUCTION 

THE  huge  slow-moving  steam  tractor  has  been  known  in 
farmland    for    many   years.     It  was    used    by  big  ranchers 
to    plow    their    broad    acres    and    to    harvest    their    grain. 
Individual   owners   also   made   their   tractors   sources   of   revenue 
by    going    around    among    smaller    farmers    to    thresh    their    oats 
and  wheat,  the  same  tractor  doing  duty  for  all  of  the  farmers 
of  a  certain  district. 

<I  Within  the  last  few  years,  however,  the  development  of  the 
gasoline  motor  and  the  dearth  of  available  farm  labor  has 
called  for  the  design  of  small  gasoline  tractors  sufficiently 
inexpensive  to  make  their  acquisition  a  possibility  for  the  aver- 
age farmer,  and  sufficiently  flexible  as  to  power  to  make  them 
economical  for  all  sorts  of  operations  about  the  farm,  from  plow- 
ing to  running  a  corn  sheller  or  a  feed  grinder.  These  small 
tractors,  while  not  having  the  flexibility  of  control  of  the  automo- 
bile, are  easily  manipulated  and  have  been  found  adaptable 
to  so  many  farm  processes  that  they  have  been  received  by 
the  farmer  with  open  arms. 

*I  Of  course,  the  farmer  for  years  has  been  so  thoroughly 
acquainted  with  the  automobile  that  he  recognizes  the  gaso- 
line tractor  as  a  friend  but  nevertheless  he  has  found  the 
mechanisms,  the  action,  and  the  management  of  his  new  assist- 
ant sufficiently  full  of  mystery  to  make  him  wish  for  a  manual 
at  his  elbow  to  help  solve  his  difficulties.  His  need  is  par- 
ticularly great  when  the  machine  stops  on  its  job  or  when  some 
part  has  to  be  replaced.  This  situation,  coupled  with  the  fact 
that  the  farmer  must  usually  be  his  own  repairman,  has  cre- 
ated a  real  need  for  an  authoritative  book  on  the  subject — 
a  book  which  will  tell  the  owner  of  a  tractor  just  what  he 
ought  to  know,  will  guide  him  in  his  selection  of  a  machine, 
and  will  tell  him  what  to  do  when  the  ignition  fails  to  work, 
when  the  carburetor  is  out  of  adjustment,  etc.  The  author 
of  this  work  has  had  a  great  deal  of  experience  in  the  gas 
engine  field  and  has  made  special  study  of  the  subject.  It 
is  the  hope  of  the  publishers  that  this  little  volume  will  suc- 
cessfully fill  the  place  for  which  it  was  designed. 

A  OPTfT  4  f\ 


CONTENTS 

Page 

Introduction 1 

Relation  of  Tractor  to  Automobile 1 

Need  of  Judgment  in  Selection  of  Tractor 1 

Classes  of  Tractors 2 

Development  of  Tractor  Industry 2 

Lack  of  Standardization 2 

Types  of  Tractors 3 

Selecting  Tractor '. 4 

Work  Done  on  Demonstration  No  Criterion 4 

Financial  Return 4 

Size  of  Farm , 5 

Size  of  Tractor 6 

ANALYSIS  OF  TRACTOR  MECHANISMS 

Tractor  Motors 9 

Steam  Tractors  vs.  Internal-Combustion  Tractors 9 

Superiority  of  Four-Cycle  Motor 9 

Motor  Parts 10 

Four-Cycle  Principle 10 

Pressure  and  Temperature 12 

Grouping  of  Motor  Parts 14 

Interrelation  of  Groups 15 

Value  of  Skilled  Operator 17 

Valves  and  Valve  Timing : 18 

Placing  of  Valves 18 

Valve  Details 18 

Camshaft  and  Timing  Gear 19 

Timing  Valves , 21 

Lead  and  Lag  of  Valve  Movement 22 

Need  of  Closely  Checking  Valves ' .  .  24 

Sixteen-Valve  Engine 24 

Fuel  Supply  System 25 

Operating  Principle  of  Internal-Combustion  Motor 25 

Fuels  Available 20 

Vaporizing  Fuel 28 

Proportion  of  Air  to  Gas 30 

Details  of  Spraying  Process 31 

Effect  of  Increasing  Speed 32 

Heating  Requirements 34 

Air  and  Fuel  Balanced. 37 

Gasoline  and  Kerosene  Carburetor.  .  39 


CONTENTS 

Page 
Fuel  Supply  System  (Continued) 

Need  for  Cleaning  Air 41 

Tractor  Air  Conditions  Very  Bad 41 

Types  of  Air  Cleaners 43 

Lubricating  System 45 

Effect  of  Temperature  and  Pressure 45 

Types  of  Lubricating  Systems 48 

Frequent  Attention  Necessary 56 

Cooling  System 56 

Heat  Efficiency  of  Motors 56 

Types  of  Cooling  Circulation 57 

Protection  of  Radiator  from  Stresses 59 

Automobile  Experience  Misleading 60 

Ignition  System 61 

Importance  of  Ignition 61 

Electric  Current 63 

Electrical  Units 63 

Conductors 63 

Circuits. 64 

Voltage  and  Amperage 66 

Low-  and  High-Tension  Currents 67 

Types  of  Ignition  Systems 68 

Low-Tension  Ignition 68 

High-Tension  Ignition 69 

Mechanisms  to  Make  and  Break  Circuit 70 

Safety  Spark  Gap 71 

Low-Tension  Magneto 72 

High-Tension  Magnetos 76 

Spark  Plugs 81 

Wiring 84 

Magneto  Impulse  Starter 84 

Types  of  Motors 87 

Wide  Range  of  Types. 87 

Horizontal  Engine 89 

Vertical  Motors 93 

Engine  Governors 97 

Need  of  Governors 97 

Centrifugal  Governors ^ 97 

Tractor  Clutches 103 

Functions  of  Clutches 103 

Types  of  Clutches 104 

Friction  Drive. .                                           109 


CONTENTS 

Page 

Tractor  Transmissions Ill 

Speed  vs.  Weight Ill 

Function  of  Transmission 112 

Wide  Range  of  Types 112 

Speeds 113 

Heavy  Types 116 

Intermediate  Types 117 

Special  Types 119 

Final  Drive 123 

TRACTOR  OPERATION 

General  Instructions 125 

Tractors  Different  in  Design  but  Alike  in  Care  Required 125 

'  Degree  of  Care  Necessary 126 

Parts  Giving  Most  Trouble 126 

Supply  of  Spares  Necessary 127 

Lubrication 129 

Motor  Lubrication 129 

Control  System  Lubrication ' 133 

Engine  Parts 134 

Engine  Bearings 134 

Valves 137 

Pistons • 142 

Carburetor 145 

Cooling  System • 149 

Horsepower  Ratings 152 

Engine  Troubles 153 

Running  Troubles 162 

Engine  Noises 166 

Clutch  and  Transmission 167 

Housing  Tractor 168 


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GASOLINE  TRACf  QRS 

PART  I 


INTRODUCTION 

Relation  of  Tractor  to  Automobile.  At  first  sight  it  appears  to 
be  rather  a  fortunate  coincidence  that  the  man  to  whom  the  trac- 
tor will  prove  of  the  greatest  benefit  is  he  who  has  found  most 
advantage  in  the  automobile — the  progressive  American  farmer. 
The  automobile  has  proved  a  veritable  godsend  to  the  farmer,  and 
there  is  no  question  but  that  he  has  thoroughly  mastered  it.  He 
appreciates  that  it  is  a  piece  of  machinery  and  as  such  can  only  be 
kept  in  satisfactory  operating  condition  by  proper  attention;  and 
further,  that  even  despite  attention  it  is  subject  to  breakdown  at 
times.  Having  acquired  this  knowledge  of  an  automobile  by  experi- 
ence, the  prospective  purchaser  of  a  tractor  naturally  feels  perfectly 
competent  to  judge  the  merits  and  demerits  of  the  various  types 
offered  and  to  give  the  one  he  buys  whatever  attention  it  may 
need  to  keep  it  operating  satisfactorily.  This  is  a  mistake  and  has 
proved  a  more  or  less  costly  one  to  many  farmers  who  have  pro- 
ceeded on  such  an  assumption.  The  tractor  is  driven  by  a  gasoline 
or  kerosene  engine,  it  has  a  gear  set,  clutch,  and  final  drive — all 
counterparts  of  the  automobile — but  it  is  not  an  automobile 
any  more  than  an  aeroplane  or  a  motorboat  is,  and  the  attention 
that  will  suffice  to  keep  an  automobile  going  wih  fall  far  short  of 
what  a  tractor  requires.  Unlike  an  automobile,  the  tractor  is 
always  operating  at  full,  or  almost  full,  load.  Moreover  it  oper- 
ates for  ten,  twelve,  or  even  eighteen  hours  a  day  under  this  load. 
Its  requirements  are  those  of  the  mogul  freight  engine  rather  than 
those  of  the  high-speed  passenger  locomotive. 

Need  of  Judgment  in  Selection  of  Tractor.  Not  every  one  can 
hope  to  operate  a  tractor  satisfactorily,  but  the  experience  of  those 
who  have  acquired  the  many  thousand  machines  turned  out  in  the 
last  few  years  shows  that,  given  proper  judgment  in  the  selection 
of  a  tractor  for  the  work  it  is  to  perform  and  the  right  kind  cf 


GASOLINE  TRACTORS 


attention  ifq.  its  neexii'ils  tyill  do  all  or  more  than  is  claimed  for  it. 
Buying  &  tj-aejtor;4nay  be>.  likened  in  some  respects  to  building  a 
house.'  "Maiiy*'  t^oplc'-neVer**  succeed  in  building  just  the  housf 
they  want  until  they  have  made  two  or  three  attempts.  This  is 
equally  true  of  tractor  purchases;  many  farmers  do  not  succeed 
the  first  time  in  buying  the  tractor  they  should  have,  but  in  the 
end  the  value  of  the  experience  gained  usually  offsets  its  cost. 

CLASSES  OF  TRACTORS 

Development  of  Tractor  Industry.  According  to  a  recent  issue 
of  a  directory  of  the  industry  one  hundred  and  thirty-five  different 
American  manufacturers  are  building  over  two  hundred  models  of 
tractors.  This  statement  holds  good  only  for  the  time  at  which  it 
is  written  since  both  the  number  cf  manufacturers  in  the  field  and 
the  number  of  models  the  old  and  the  new  entrants  are  turning 
out  are  constantly  on  the  increase.  The  use  of  tractors  on  large 
farms  dates  back  almost  half  a  century,  but  up  to  less  than  ten 
years  ago  they  were  all  of  the  steam-driven  type.  Their  first  cost 
as  well  as  the  expense  of  maintenance  made  them  practical  only 
on  very  large  farms  where  skilled  labor  is  constantly  employed. 
This  bit  of  history  is  mentioned  merely  to  emphasize  the  infancy 
of  the  industry  as  it  now  exists,  a  factor  that  makes  it  exceedingly 
difficult  to  classify  the  product  of  all  the  manufacturers  in  the 
field  and  even  harder  for  the  prospective  purchaser  to  make  his 
selection  of  a  machine.  The  business  of  building  gasoline-  and  oil- 
driven-  tractors  only  dates  back  to  about  1910,  and  for  the  first 
five  years  of  its  existence  its  progress  was  not  very  rapid.  Conse- 
quently it  is  only  during  the  last  four  years  or  so  that  most  of  the 
many  manufacturers  mentioned  have  entered  the  field  in  response 
to  the  great  demand  for  tractors  on  the  part  of  the  farmers,  caused 
by  the  acute  shortage  of  farm  labor  and  the  corresponding  increase 
in  wages. 

Lack  of  Standardization.  When  an  industry  comes  into 
existence  almost  overnight,  as  in  the  present  instance,  every  manu- 
facturer proceeds  along  individual  lines  in  the  design  of  his  machine 
with  the  result  that  the  divergence  in  types  is  almost  as  note- 
worthy as  the  number  competing.  The  tractor  industry  now  finds 
itself  in  about  the  same  position  as  did  the  automobile  industry 


II 


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§   8 


GASOLINE  TRACTORS  3 

fifteen  years  earlier  in  that  the  machines  differ  widely  in  design 
and  construction,  horsepower  ratings  bear  little  relation  to  the 
dimensions  or  speed  of  the  motor,  and  weights  for  the  same  horse- 
power are  often  far  apart.  There  is  accordingly  an  entire  lack  of 
standardization  where  any  of  the  essentials  are  concerned  though 
efforts  to  remedy  this  situation  by  the  Society  of  Automotive 
Engineers  are  already  well  under  way.  It  is  scarcely  to  be 
expected,  however,  that  the  recommendations  adopted  can  come 
into  general  use  for  two  or  three  years  at  least.  Meanwhile,  many 
thousands  of  tractors  are  being  turned  out  annually,  and  the  pro- 
spective purchaser  must  make  his  selection  of  a  machine  from 
those  offered,  since  conditions  make  it  impossible  to  wait  for  the 
perfected  tractor  to  be  produced  several  years  from  now. 

Types  of  Tractors.  Regarded  from  the  mechanical  standpoint, 
the  large"  number  of  machines  now  being  built  may  be  classified  in 
groups  according  to  some  feature  of  design,  such  as  the  type  of 
motor  employed,  the  method  of  transmitting  the  power,  the  man- 
ner of  securing  traction,  and  the  number  of  wheels,  where  the  lat- 
ter are  used.  For  example,  when  classified  according  to  type  of 
motor,  there  would  be  a  group  consisting  of  those  tractors  using  a 
slow-speed  two-cylinder  engine  adapted  from  stationary-engine 
practice,  and  a  second  group  of  those  employing  a  high-speed  four- 
or  six-cylinder  motor  designed  along  lines  that  have  been  made 
familiar  on  the  automobile.  When  classified  according  to  trans- 
mission of  power,  the  tractors  using  a  drive  through  a  clutch, 
which  are  in  the  majority,  would  fall  in  one  group  and  those 
employing  a  friction  type  of  drive  in  another.  On  the  basis  of  the 
method  of  obtaining  traction  we  would  have  a  group  consisting  of 
tractors  employing  wheels,  also  in  the  majority,  and  a  group  com- 
posed of  the  so-called  caterpillar,  or  tracklaying,  type  and  its 
numerous  modifications.  A  subdivision  of  the  class  using  wheels 
can  be  made  to  cover  three-  and  four-wheel  types  sinct  many 
machines  differ  chiefly  in  this  respect.  As  a  matter  cf  fact,  sub- 
divisions of  practically  every  one  of  these  classes  are  possible. 
For  instance,  in  some  three-wheel  machines  there  are  two  driving 
wheels,  while  in  others  but  one  is  employed.  These  numerous 
differences  are  cited  merely  to  point  out  the  great  rarge  of  varia- 
tion that  exists. 


4  GASOLINE  TRACTORS 

SELECTING  TRACTOR 

Work  Done  on  Demonstration  No  Criterion.  Involving,  as  it 
does,  an  investment  larger  than  that  of  almost  any  other  single 
farm  machine,  the  selection  of  a  tractor  should  be  made  the  sub- 
ject of  as  much  study  and  investigation  as  the  prospective  buyer 
can  possibly  give.  One  of  the  commonest  fallacies  in  tractor  buy- 
ing is  to  judge  the  merits  of  the  machine  by  the  class  of  work  it 
does,  the  term  "work"  in  this  connection  being  applied  almost 
entirely  to  plowing  since  the  latter  represents  the  heaviest  service 
to  which  the  tractor  is  put.  It  should  be  borne  in  mind  that  the 
tractor  is  nothing  more  than  the  motive  power,  and  neither  its 
reliability  nor  its  value  as  a  farm  machine  can  be  judged  from  the 
character  of  the  plowing  it  does  on  a  demonstration.  Good  or 
poor  plowing  depends  entirely  upon  the  plow  itself  and  the  methods 
used  in  its  handling,  so  that  a  poor  tractor  properly  hitched  to  the 
right  type  of  plow  and  in  the  hands  of  a  skilled  operator  will  do 
better  work  than  the  best  tractor  that  can  be  built  will  turn  out 
when  handled  improperly.  The  method  of  hitching  the  plows  to 
the  tractor  governs  not  only  the  quality  of  work  turned  out  but 
likewise  the  amount  of  power  consumed  in  doing  it,  granting  that 
the  right  type  of  plow  is  being  used  for  the  soil  under  considera- 
tion. It  would  be  just  as  sensible  to  judge  the  value  of  a 
team  of  horses  by  the  character  of  the  furrows  they  turned  in 
plowing. 

Financial  Return.  It  has  become  customary  to  criticize  Amer- 
ican farming  methods  as  compared  with  European  solely  upon  the 
difference  in  production  per  acre,  the  fact  that  the  application  of 
intensive  cultivation  by  hand  labor  to  very  small  areas  is  account- 
able for  the  disparity  being  lost  sight  of  entirely.  American  agri- 
cultural methods  produce  more  per  acre  for  each  man  employed 
than  is  grown  anywhere  else  in  the  world,  and  this  is  due  solely  to 
the  application  of  farm  machinery  to  production  on  a  larger  scale 
than  has  ever  been  attempted  abroad.  This  has  a  direct  bearing 
on  the  purchase  of  a  tractor,  since  the  capital  required  for  the  lat- 
ter must  be  invested  for  one  of  two  reasons:  either  the  tractor 
will  enable  its  owner  to  cultivate  the  same  number  of  acres  more 
economically,  or  it  will  place  him  in  a  position  to  cultivate  a 
greater  number  of  acres  with  the  same  number  of  "hands." 


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II 


GASOLINE  TRACTORS  5 

The  impression  has  been  more  or  less  general  that  the  first  of 
these  two  reasons,  "It  will  do  the  work  cheaper,'*  is  the  chief  one 
for  purchasing  a  tractor.  Investigations  carried  out  by  the  Depart- 
ment of  Agriculture,  however,  have  shown  that  this  reason  is  not 
valid.  Taking  into  account  the  capital  outlay  required,  the  cost  of 
operation,  and  the  depreciation,  and  considering  the  average  life  of 
a  tractor  as  seven  or  eight  years,  it  has  been  found  that  plowing 
cannot  be  done  any  more  cheaply  with  a  tractor  than  with  horses, 
but  that  the  use  of  the  tractor  does  enable  the  farmer  to  cultivate 
a  substantially  increased  number  of  acres  writh  the  same  number 
of  men.  Out  of  the  large  number  of  farms  investigated,  a  major- 
ity of  the  owners  found  it  necessary  to  increase  their  acreage  after 
purchasing  a  tractor  in  order  to  use  their  machines  most  effi- 
ciently. In  other  words,  the  same  crops  could  not  be  raised  any 
more  cheaply  with  the  tractor  than  without  it,  but  much  larger 
crops  could  be  raised  by  increasing  the  acreage  under  cultivation. 
This  naturally  applies  more  particularly  to  small  farms,  by  which 
is  meant  those  of  150  acres  or  less,  taking  the  country  as  a  whole, 
since  what  is  considered  a  small  farm  in  the  Middle  West  would 
be  thought  quite  the  contrary  in  New  England. 

Size  of  Farm.  It  goes  without  saying  that  a  tractor  will  not 
prove  a  profitable  investment  on  farms  of  such  a  size  that  all  the 
land  available  for  cultivation  may  be  as  easily  worked  by  horses 
in  the  time  allowed,  which  classification  would  cover  all  farms  hav- 
ing 100  acres  or  less  of  cultivable  land  since  only  a  portion  of  the 
total  acreage  is  open  to  cultivation  on  any  farm.  Many  farmers 
consider  the  purchase  of  a  tractor  on  the  assumption  that  its  excess 
capacity  can  be  taken  care  of  by  doing  "custom  work,"  or  plowing 
for  neighbors.  In  a  number  of  cases  of  this  kind  that  were  inves- 
tigated the  charge  made  for  this  work  was  not  sufficient  to  leave  a 
profit  after  deducting  the  cost  of  operation  and  the  interest  on  the 
investment,  so  that  the  farmer  would  have  been  better  off  without 
undertaking  this  extra  work.  As  a  means  of  paying  for  the  trac- 
tor when  the  owner's  farm  is  not  sufficiently  large  to  absorb  its 
full  capacity,  this  practice  did  not  show  a  profit  that  would  war- 
rant the  investment  in  a  tractor,  since,  as  before  stated,  the 
charges  were  too  low  to  cover  the  cost  of  operation,  while 
increasing  the  rates  to  a  point  that  would  leave  a  profit  would 


6  GASOLINE   TRACTORS 

result  in  a  falling  off  in  the  demand  as  the  renter  could  do  the 
same  work  for  considerably  less  with  horses. 

Judging  from  the  results  of  the  investigations  in  question,  it 
will  not  pay  the  owner  of  a  150-acre  farm  of  which  not  more  than 
100  are  cultivable  to  invest  in  a  tractor  unless  he  can  add  from  20 
to  50  acres  to  that  under  cultivation.  This,  of  course,  is  a  general 
statement  that  may  be  subject  to  modification  in  numerous 
instances  where  specially  favorable  conditions  make  the  use  of  a 
machine  advantageous.  But  this  statement  as  well  as  the  pre- 
ceding matter  is  intended  chiefly  to  emphasize  to  the  prospective 
purchaser  of  a  tractor  the  fact  that  it  is  unwise  to  make  the  invest- 
ment required  in  anticipation  of  doing  the  same  amount  of  work 
much  more  economically  than  it  can  be  performed  with  horses. 

Size  of  Tractor.  First  cost  is  naturally  the  chief  item  con- 
sidered in  the  purchase  of  a  tractor,  and  in  this  connection  true 
economy  is  to  be  found  in  the  selection  of  a  machine  that  is  not 
only  of  good  quality,  properly  designed  and  well  built  for  the 
work  it  is  to  do,  but  that  likewise  has  ample  capacity  to  handle  it 
without  overloading.  It  will  prove  as  expensive  in  the  long  run  to 
pay  for  a  good  small  machine  that  must  be  overloaded  to  do  the 
work  required  as  to  buy  a  cheap  machine  of  any  size.  In  either 
case  the  repair  bills  and  the  time  lost  through  delays  at  the  height 
of  the  season  are  apt  to  make  the  buyer  regret  his  choice,  if,  in 
fact,  he  is  not  led  to  condemn  tractors  altogether.  In  this  con- 
nection, however,  the  skill  and  experience  of  the  operator  are  fac- 
tors which  have  a  very  important  bearing  on  the  successful  use  of 
the  machine  and  largely  govern  the  amount  of  time  that  it  is  out 
of  service  due  to  breakdowns.  This  is  dwelt  upon  at  greater 
length  in  later  paragraphs. 

Tests  have  demonstrated  that  at  the  maximum  speed  of  plow- 
ing recommended  for  all  tractors,  that  is,  2J  to  2J  miles  per  hour, 
a  two-gang  plow  will  not  cover  much  more  ground  in  a  day  of  ten 
hours  when  drawn  by  a  machine  than  when  pulled  by  horses.  In 
other  words,  the  advantage  of  the  tractor-drawn  two-gang  plow 
over  horse  work  is  so  small  that  it  usually  does  not  pay  to  buy  a 
machine  whose  maximum  capacity  is  two  plows.  Whether  it  be  a 
tractor  or  any  other  type  of  machine,  it  is  not  good  practice  to 
depend  upon  running  it  at  its  maximum  capacity  continuously. 


r 


II 


BORING  THREE-WHEEL  TRACTOR  WITH  FORWARD  DRIVE  AND 
UNDERSLUNG  PLOWS 


HEAVY  THREE-WHEEL  TYPE  OF  TRACTOR 


GASOLINE  TRACTORS  7 

The  machine  will  not  do  as  good  work  and  it  will  be  much  more 
subject  to  frequent  breakdown  than  where  it  has  power  in  reserve 
to  meet  emergencies  that  will  seriously  overload  a  machine  that  is 
already  working  at  its  full  output. 

The  number  of  plows  that  any  given  machine  is  capable  of 
pulling  depends  upon  so  many  other  factors  besides  its  power  rat- 
ing that  it  is  often  misleading  to  term  a  tractor  a  two-,  three-,  or 
four-plow  machine,  as  the  case  may  be.  The  depth  of  the  furrow, 
the  character  and  condition  of  the  soil,  and  the  method  of  hitching 
all  influence  this  to  such  an  extent  that  a  machine  capable  of  pull- 
ing three  plows  under  favorable  conditions  might  make  a  very 
poor  job  with  two  where  the  soil  conditions  were  not  so  good  or 
the  plows  were  not  properly  hitched.  , 

Margin  of  Safety  Needed.  It  should  be  borne  in  mind  that 
any  machine  will  give  the  most  satisfactory  service  and  have  the 
longest  useful  life  when  operated  continuously  at  not  more  than  75 
per  cent  of  its  rated  capacity.  Expense  incident  to  delays  as  well 
as  the  cost  of  repairs  will  accordingly  be  minimized  when  a 
machine  larger  than  is  actually  required  is  selected  and  is  operated 
at  less  than  its  full  capacity.  Experienced  tractor  operators  have 
proved  this  in  many  instances  by  investing  in  four-plow  machines 
and  pulling  but  three  plows.  It  does  not  pay  to  load  a  machine 
to  its  limit  since  it  cannot  carry  such  a  load  continuously  and  give 
satisfactory  service,  so  that  in  selecting  a  tractor  the  chief  points 
to  bear  in  mind  are  not  to  buy  a  lightly  or  cheaply  built  machine; 
and  not  to  select  a  machine  so  small  that  it  can  only  do  the  work 
required  by  working  continuously  at  full  load. 

Power  for  Belt  Work.  While  plowing  constitutes  more  than 
one-half  the  work  for  which  the  tractor  is  required,  it  would 
pay  few  farmers  to  invest  in  a  machine  for  that  purpose  alone. 
All  tractors  are  designed  to  be  used  as  stationary  power  plants  as 
well,  and  one-third  or  more  of  the  service  demanded  of  them  con- 
sists of  driving  other  machines,  such  as  threshers  or  ensilage  cut- 
ters, or,  as  it  is  usually  termed,  belt  work.  Unless  a  machine  has 
ample  power  for  this,  it  will  not  be  found  satisfactory  since  there 
is  usually  a  tendency  under  such  conditions  to  load  it  to  the  stall- 
ing point  and  when  a  cutter  has  been  "choked  down,"  much  val- 
uable time  is  lost  in  getting  it  under  way  again. 


8  GASOLINE   TRACTORS 

A  tractor  that  is  not  powerful  enough  to  do  all  the  work 
required  of  it  is  not  likely  to  prove  a  satisfactory  investment, 
though  an  error  may  also  be  made  by  going  to  the  other  extreme 
and  selecting  a  machine  of  such  a  size  that  it  is  too  expensive  to 
operate  on  many  of  the  jobs  that  a  tractor  of  the  proper  size 
would  perform  economically. 

Factors  Governing  Capacity.  Why  a  machine  that  will  pull 
three  plows  very  satisfactorily  under  some  conditions  will  with 
difficulty  do  good  work  with  only  two  bottoms  in  other  locations 
will  be  readily  apparent  from  a  consideration  of  the  difference  in 
drawbar  pull  required  for  plowing  different  soils.  The  average 
resistance  of  soils  is  given  approximately  in  Table  I. 

While  the  figures  in  Table  I  have  been  drawn  from  experience, 
the  draft  of  a  tractor  plow  can  only  be  approximated,  since  the 
condition  of  the  plow  itself  and  the  method  of  hitching  are  of  the 
greatest  importance.  The  figures  given  are  based  upon  the  sup- 
position that  the  plow  is  clean,  sharp,  and  properly  hitched  so  as 
to  cut  easily.  When  a  plow  is  dull  or  does  not  scour  well,  the 
power  required  to  draw  it  will  be  substantially  increased.  This  is 
equally  true  when  a  plow  is  not  leveled  or  is  out  of  line  in  any  way. 

The  draft  likewise  increases  in  proportion  to  the  grade  and 
the  figures  given  are  based  upon  plowing  on  level  ground.  For 
each  1  per  cent  rise  in  grade,  that  is,  for  each  foot  of  vertical  lift 
in  each  100  feet  of  horizontal  travel,  1  per  cent  of  the  combined 
weight  of  the  tractor  and  the  plows  must  be  added  to  the  draft. 
For  example,  assume  a  tractor  weighing  5000  pounds  and  hauling 
four  plows  each  weighing  250  pounds,  making  the  total  6000  pounds: 
the  maximum  draft  of  the  four  plows  in  corn  stubble,  plowing  6 
inches  deep,  would  be  3200  pounds,  to  which  it  would  be  necessary 
to  add  60  pounds  for  each  1  per  cent  increase  in  grade.  Even  on 
rolling  prairie  land,  which  is  ordinarily  thought  of  as  being  level, 
the  dips  and  hollows  often  represent  10  per  cent  grades  for  short 
distances,  and  in  this  case  they  would  necessitate  adding  600  pounds 
to  the  draft  required. 

When  planning  to  buy  a  tractor  to  do  certain  work,  keep  the 
figures  given  in  the  table  in  mind;  consider  the  character  of  the 
soil,  the  grades,  the  depth  of  the  furrow,  and  the  horsepower  rat- 
ing of  the  machine  desired — and  it  is  always  well  to  discount  that 


GASOLINE  TRACTORS 


TABLE  I 
Average  Resistance  of  Soils 


Soil 

Pounds  per 
Square  Inch 

6  Inches 
Deep 

8  Inches 
Deep 

Sandy  loam 

4-6 

600-  800 

750-  950 

Corn  stubble 

6 

700-  800 

900-1000 

Wheat  stubble 

8 

800-  900 

1000-1100 

Light  clay 

12 

800-1200 

1000-1400 

Medium  clay 

14 

900-1400 

1200-1500 

Heavy  clay  in  good  plowing  condition 

16 

1600-2000 

1800-2100 

Sod  or  heavy  clay,  medium  moisture 

18 

2500-3000 

2700-3100 

Gumbo  —  dry,  hard 

36 

2600-3200 

2800-3300 

horsepower  rating  somewhat.  It  will  also  pay  to  keep  these 
figures  in  mind  when  the  over-enthusiastic  salesman  begins  to  make 
claims. 

ANALYSIS  OF  TRACTOR  MECHANISMS 

TRACTOR   MOTORS 

Steam  Tractors  vs.  Internal=Combustion  Tractors.  Although 
tractors  have  been  used  in  this  country  for  almost  half  a  century, 
they  were  all  steam  driven  until  less  than  ten  years  ago,  so  that 
the  present  widespread  and  rapidly  increasing  adoption  of  the 
tractor  is  due  to  the  remarkable  development  of  the  internal- 
combustion  motor,  which,  in  turn,  is  largely  the  result  of  the  great 
strides  the  automobile  industry  has  made  since  1900.  The  present 
work  is  accordingly  confined  to  tractors  with  such  motors  since, 
although  steam  tractors  will  continue  to  be  used  on  some  of  the 
very  large  farms  on  which  they  have  been  employed  so  long,  they 
are  not  available  to  the  average  purchaser  of  a  tractor  and,  at 
best,  it  will  be  only  a  matter  of  a  comparatively  few  years  before 
they  will  have  been  displaced  by  the  internal-combustion  type  in 
most  parts  of  the  country. 

Superiority  of  Four=Cycle  Motor.  The  experience  of  the  auto- 
mobile manufacturer  as  well  as  that  of  the  stationary  oil-engine 
builder  has  demonstrated  that  of  the  several  types  of  internal- 
combustion  motors  that  may  be  used  that  based  upon  the  so-called 
four-cycle  method  of  operation  combines  the  fewest  drawbacks 
with  the  greatest  number  of  advantages  and  is  accordingly  the 


10  GASOLINE  TRACTORS 

most  practical  for  general  use.  The  two-cycle  motor  has  never 
proved  successful  owing  to  its  inefficiency  where  fuel  consump- 
tion is  concerned,  while  other  types  involve  the  use  of  excessive 
weights  for  the  power  generated. 

Motor  Parts.  Assuming  the  motor  to  have  but  one  cylinder, 
a  four-cycle  motor  consists  of  a  cylinder,  inlet  valve  and  exhaust 
valve,  piston,  piston  rings,  piston  pin,  connecting  rod,  crankshaft 
and  bearings,  flywheel,  camshaft,  valve  springs  and  crankcase. 
Its  accessories  are  a  carburetor  (or  fuel-mixing  device),  magneto  or 
other  method  of  generating  electric  current,  spark  plug  for  igniting 
the  fuel,  lubricating  system,  cooling  system,  and  the  necessary 
piping  for  supplying  lubricating  oil  and  for  conducting  the  cooling 
water  between  the  cylinder  jackets  and  the  radiator,  the  fuel  mix- 
ture from  the  carburetor  to  the  combustion  chamber  of  the  cylin- 
der, and  the  exhaust  gases  away  from  the  latter  after  they  have 
been  burned.  A  circulating  pump  may  or  may  not  form  a  part  of 
the  cooling  system  according  to  the  method  of  circulation  employed. 
These  auxiliaries,  plus  a  fan  to  assist  in  the  cooling  of  the  water  or 

011  in  the  radiator  of  the  cooling  system,  complete  the  motor  and 
the  addition  of  any  number  of  cylinders  only  involves  the  duplica- 
tion of  those  parts  directly  attached  to  or  working  in  the  cylinder, 
such  as  valves,  pistons,  and  connecting  rods  with,  of  course,  the 
provision  of  an  additional  crankthrow  on  the  crankshaft  for  each 
additional  cylinder. 

Four=Cycle  Principle.  Intake  Stroke.  The  operation  of  the 
motor  is  based  upon  a  cycle,  or  recurrence  of  operations,  consisting 
of  four  distinct  parts.  Starting  with  the  piston  at  the  upper  dead 
center,  the  first  of  these  operations  is  the  intake,  or  suction, 
stroke.  The  inlet  valve  has  been  opened  through  the  revolution  of 
the  camshaft  bringing  the  cam  in  contact  .wjth  the  valve  tappet 
and  raising  the  valve  off  its  seat,  Fig.  1.  The  piston  is  a  gas- 
tight  fit  in  the  cylinder,  being  sealed  by  the  piston  rings,  which 
press  out  against  the  cylinder  walls,  and  by  the  presence  of  a 
film  of  lubricating  oil  between  the  piston  and  the  cylinder.  The 
downward  travel  of  the  piston  accordingly  creates  a  partial  vacuum 
(negative  pressure,  or  less  than  atmospheric)  in  the  cylinder,  and 
the  atmospheric  pressure  (14.7  pounds  at  sea  level),  acting  upon 
the  liquid  fuel  in  the  carburetor,  forces  the  liquid  up  through  the 


GASOLINE  TRACTORS 


11 


spray  nozzle  of  the  carburetor  and  also  draws  a  predetermined 
volume  of  air  up  through  this  spray,  thus  forming  a  fuel  mixture 
which  is  forced  into  the  cylinder.  The  action  of  the  piston  on 
this  first  part  of  the  cycle  is  exactly  the  same  as  that  of  a  pump 
in  drawing  water  out  of  a  well.  The  water  is  forced  up  into  the 
pump,  following  the  plunger  owing  to  the  decreased  pressure  in  the 
pump  barrel  caused  by  the 
stroke  of  the  plunger  and  to 
the  outside  pressure  of  the  air 
on  the  surface  of  the  water. 
Compression  Stroke. 
When  the  piston  reaches  the 
limit  of  its  travel,  or  lower 
dead  center,  the  inlet  valve 
closes  and  the  piston  in  rising 
then  compresses  the  fuel  mix- 
ture against  the  head  of  the 
cylinder,  the  valves  also  being 
gas  tight.  This  is  the  second 
part  of  the  cycle,  or  the  com- 
pression stroke,  and  gives  to 
the  fuel  mixture  what  is  known 
as  the  initial  compression.  This 
stroke  has  an  important  bear- 
ing on  the  power  output  of  the 
motor  since  it  renders  the  com- 


bustion of  the  fuel  more  rapid 
and  complete  and  also  in- 
creases the  pressure  developed 

when  the  Charge  is  fired.  The  Figs-  1-4-  Strokes  of  Four-Part  Cycle:  1.  Intake; 
^  ^  f  &  t  m  2.  Compression;  3.  Power;  4.  Exhaust 

initial  compression  used  in  the 

average  gasoline  motor  ranges  from  50  to  80  pounds  per  square  inch, 
and  the  higher  it  is,  the  more  power  the  motor  develops,  other 
factors  such  as  cylinder  dimensions  and  number  of  cylinders  being 
the  same.  In  the  case  of  gasoline,  however,  this  initial  pressure 
is  limited  to  90  pounds  per  square  inch  since  the  heat  generated 
by  compression  above  that  point  would  cause  the  ignition  of  the 
mixture.  Tn  kerosene,  alcohol,  or  low-grade  fuel  engines,  it  may 


12  GASOLINE   TRACTORS 

be  much  higher,  but  in  this  case  a  compression  release  must  be 
fitted  to  the  engine  in  order  that  it  may  be  turned  over  by  hand 
for  starting. 

Power  Stroke.  The  third  part  of  the  cycle  begins  with  the 
firing  of  the  charge  by  the  passage  of  a  spark  at  the  plug,  and 
the  piston  then  starts  downward  on  the  power  stroke.  Just  before  the 
piston  reaches  the  lower  dead  center  on  this  stroke,  the  exhaust 
valve  is  lifted  by  the  camshaft  and  the  remaining  pressure  in  the 
cylinder,  which  cannot  be  utilized  for  driving  the  piston,  is  allowed 
to  escape.  A  very  large  part  of  the  heat  value  of  the  fuel  is 
wasted  in  this  manner  through  the  exhaust,  but  the  drop  from  the 
very  high  pressure  at  the  moment  of  ignition  is  so  rapid  that  no 
advantage  is  to  be  gained  from  lengthening  the  stroke  beyond  a 
certain  point  in  an  attempt  to  utilize  a  greater  percentage  of  the 
pressure. 

Exhaust  Stroke.  The  following  upward  movement  of  the  pis- 
ton is  termed  the  exhaust  stroke  and  serves  to  clear  the  cylinder  of 
the  remaining  burned  gases  in  preparation  for  the  succeeding  suc- 
tion stroke,  which  recommences  the  cycle.  Although  it  is  one  of 
the  three  idle  strokes  of  the  four-cycle  method  of  operation,  the 
exhaust  stroke  is  quite  as  important  as  those  which  precede  it 
since,  unless  the  cylinder  is  swept  clear  of  the  burned  gases  of  the 
previous  explosion  as  completely  as  possible,  a  volume  of  dead  gas 
is  left  to  occupy  space  which  should  be  filled  with  fresh  fuel  and 
the  amount  of  power  developed  on  succeeding  strokes  is  reduced 
in  proportion.  This  is  one  of  the  chief  defects  of  the  two-cycle 
method  of  operation,  in  which  compression  immediately  follows 
the  power  stroke,  there  being  no  exhaust  stroke  or  suction  stroke. 
As  a  result,  a  considerable  percentage  of  the  cylinder  space  is 
always  filled  with  burned  gases  and  the  time  available  for  the 
power  stroke  is  so  short  that  part  of  the  fresh  gas  escapes  unburned. 
In  the  four-cycle  method,  upon  the  completion  of  the  exhaust 
stroke,  the  exhaust  valve  closes  and  the  inlet  valve  opens,  begin- 
ning a  new  cycle.  The  relative  positions  of  the  piston  and  the 
valves  during  the  compression,  power,  and  exhaust  strokes  are 
shown  in  Figs.  2,  3,  and  4. 

Pressure  and  Temperature.  While  even  the  most  skilled 
operator  of  a  traction  engine  need  not  be  conversant  with  the 


GASOLINE   TRACTORS  13 

intricacies  of  its  design  nor  with  the  scientific  aspect  of  its  opera- 
tion, a  knowledge  of  what  goes  on  inside  the  cylinder  will  be 
found  an  aid  to  a  clearer  understanding  of  the  engine  itself  and 
the  principles  on  which  it  works.  The  internal-combustion  motor 
is  a  heat  engine  pure  and  simple,  and  each  part  of  its  cycle  is 
attended  by  an  increase  or  decrease  in  pressure  and  temperature. 
One  is  a  function  of  the  other,  a  given  degree  of  pressure  resulting 
in  an  equivalent  rise  in  temperature,  and  this  fact  is  taken  advan- 
tage of  in  determining  the  pressure  and  the  temperature  in  the 
cylinder  by  means  of  an  indicator,  the  use  of  which  need  not  be 
described  here  since  it  is  only  used  by  designers  in  the  shop. 

Range  of  Pressure  and  Temperature.  Some  idea  of  the  great 
range  of  pressure  and  temperature  inside  the  cylinder  during  but 
two  parts  of  the  cycle,  the  compression  and  power  strokes,  may  be 
gained  by  assuming  that  the  motor  is  operating  on  a  summer  day 
with  the  surrounding  temperature  at  70°  F.  The  temperature  of 
the  entering  mixture  will  then  be  raised  to  approximately  100°  F. 
or  more  through  the  use  of  hot  air  in  forming  the  fuel  mixture  by 
taking  the  air  supply  from  a  "stove"  attached  to  the  exhaust 
manifold  or  by  using  exhaust  gases  direct  from  the  engine  and 
also  through  having  a  water  jacket  surrounding  the  intake  mani- 
fold. Without  these  heating  devices  the  mixture  would  be  con- 
siderably cooler  than  the  atmosphere  since  the  conversion  of  the 
liquid  fuel  into  a  vapor  is  attended  by  the  abstraction  of  heat 
from  the  air.  Assuming  that  the  engine  has  been  running,  the 
end  of  the  previous  exhaust  stroke  leaves  the  interior  of  the 
cylinder  at  a  temperature  of  approximately  260°  F.  and  the  incom- 
ing mixture  is  further  heated  by  contact  with  the  cylinder  walls 
and  the  piston  head.  At  the  moment  of  intake  the  pressure  in  the 
cylinder  is  slightly  less  than  atmospheric.  During  the  compression 
stroke  this  pressure  is  raised  to  50-85  pounds,  depending  upon  the 
amount  of  initial  compression  given,  and  the  temperature  rises  to 
a  point  between  800°  and  900°  F.  Upon  the  gases  being  ignited, 
their  tremendous  expansion  in  the  confined  space  raises  the  pres- 
sure to  225-250  pounds  per  square  inch  with  an  increase  in  tem- 
perature ranging  from  2500°  to  4000°  F.,  depending  upon  the 
character  of  the  fuel  used.  This  pressure  decreases  very  rapidly 
as  the  piston  moves  outward  on  the  power  stroke,  the  so-called 


14  GASOLINE  TRACTORS 

terminal  pressure,  that  is,  the  pressure  at  the  end  of  the  stroke 
when  the  exhaust  valve  opens,  reaching  40  to  50  pounds  with  a 
temperature  of  approximately  1000°  F.  The  exhaust  stroke 
lowers  the  pressure  to  approximately  that  of  the  surrounding 
atmosphere  with  a  decrease  in  temperature  that  is  governed  to  some 
extent  by  the  length  of  time  that  the  engine  has  been  running. 

Effect  of  High  Temperature.  The  extreme  range  of  tempera- 
tures inside  the  cylinder  should  impress  upon  the  operator  of  a 
tractor  engine  the  necessity  for  prompt  attention  if  anything  goes 
wrong.  For  example,  in  the  presence  of  such  great  heat  as  is 
developed  by  the  explosion  it  will  be  evident  that  failure  of  the 
lubrication  or  of  the  cooling  system  can  cause  serious  damage  in  a 
very  brief  period.  Pistons  will  score  and  scratch  the  cylinder 
walls,  valves  will  warp, .  bearings  will  be  burned  out,  and  finally 
the  pistons  will  bind  hard  and  fast,  all  in  the  short  space  of  a  few 
minutes.  In  fact,  five  minutes  will  suffice  to  cause  damage,  the 
repairing  of  which  will  take  a  week  and  will  represent  a  bill  of 
three  figures. 

Grouping  of  Motor  Parts.  Mechanical  Group.  The  parts  nec- 
essary to  a  four-cycle  motor,  whether  of  one  or  several  cylinders, 
have  already  been  outlined.  Upon  studying  these,  it  will  be 
apparent  that  they  may  be  divided  into  groups  and  that  each 
group  has  as  its  object  the  carrying  out  of  a  certain  function  in 
the  operation  of  the  motor.  The  foundation  of  all  the  groups  is 
naturally  the  chief  mechanical  group  consisting  of  the  cylinders, 
valves,  pistons,  connecting  rods,  crankshaft,  camshaft,  crankcase, 
and  flywheel.  The  functions  of  this  group  are  to  provide  a 
container  in  which  the  fuel  may  be  compressed  and  ignited  and 
moving  parts  against  which  the  force  of  the  explosion  may  act — 
first,  to  produce  linear  motion  in  the  stroke  of  the  piston  and,  sec- 
ond, to  convert  that  motion  into  rotary  motion  at  the  crankshaft. 

Auxiliary  Groups.  All  the  other  groups  really  consist  of 
auxiliaries,  such  as  the  carburetor,  heating  devices,  and  intake  and 
exhaust  manifolds,  designed  to  mix  the  fuel  with  the  proper  pro- 
portion of  air,  warm  it,  conduct  it  to  the  cylinders,  and  lead  it 
away  from  the  latter  "after  it  has  been  burned.  These  parts  con- 
stitute the  second  group,  or  fuel-supply  system.  The  third  group 
consists  of  the  apparatus  for  igniting  the  fuel  in  the  cylinders  and 


GASOLINE   TRACTORS  15 

is  represented  by  the  magneto  (or  other  method  of  generating 
electric  current),  the  spark  plugs,  the  connecting  cables,  and  any 
distributing  or  timing  devices  necessary  when  a  battery  instead  of 
a  magneto  is  employed.  The  fourth  group  is  represented  by  the 
lubricating  system,  the  function  of  which  is  to  supply  oil  to  all 
the  moving  parts;  while  the  fifth  group  is  the  cooling  system,  con- 
sisting of  the  water  jackets  of  the  cylinders,  the  pump,  the  radia- 
tor, and  the  piping  connections.  On  the  traction  engine  there  are 
further  auxiliaries  not  necessary  on  an  automobile  engine,  namely: 
the  governor  and  the  air  cleaner.  A  large  part  of  the  work  of  the 
tractor  consists  in  serving  as  a  stationary  power  plant,  and  while 
doing  belt  work  it  is  necessary  that  a  steady  engine  speed  be 
maintained  under  a  wide  range  of  load.  Unless  the  engine  were 
automatically  governed  under  such  conditions,  it  would  stall  when 
the  load  was  increased  and  race  when  the  load  was  relieved;  and 
racing  would  be  dangerous  to  the  engine  itself  owing  to  the  great 
stresses  set  up  by  the  high  speed.  While  not  constituting  a  group 
in  itself,  the  governor  may  be  included  in  a  further  group  consist- 
ing of  the  control  system,  in  which  the  throttle  and  the  spark 
levers  represent  the  hand  control,  and  the  governor  the  automatic 
control  of  the  engine. 

Interrelation  of  Groups.  It  will  be  apparent  upon  a  little 
study  of  these  different  groups,  or  systems,  that  all  are  equally 
essential  to  the  operation  of  the  motor  and  that  precedence  cannot 
be  accorded  to  any  one  as  compared  with  the  others  since  the 
failure  of  any  one  would  prevent  the  functioning  of  the  rest.  An 
understanding  of  the  relations  that  these  groups  bear  to  one 
another  will  go  a  long  way  toward  making  clear  the  principles  on 
which  the  engine  operates  and  also  the  manner  in  which  the  differ- 
ent systems  must  work  together  in  order  that  it  may  run  satisfac- 
torily. The  interdependent  functions  of  the  groups  are  considered 
at  some  length  in  the  following  paragraphs. 

Mechanical  Group.  Unless  the  pistons  are  free  to  move  in  the 
cylinders  and  the  crankshaft  and  the  connecting  rods  on  their 
bearings,  no  movement  can  result.  This  free  movement  of  the 
pistons  and  other  working  parts  is  entirely  dependent  upon  the 
lubricating  system  maintaining  a  constant  supply  of  oil  on  all  con- 
tacting surfaces.  But  unless  the  cooling  system  continues  to 


16  GASOLINE   TRACTORS 

function  properly,  the  fact  that  the  lubricating  system  is  working 
will  not  keep  the  motor  running  since  the  oil  will  be  burned  up  on 
coming  in  contact  with  the  cylinder  walls  owing  to  the  high  tem- 
perature inside  the  cylinder. 

Fuel-Supply  System.  Air  must  be  drawn  through  the  carbu- 
retor and  mixed  with  the  spray  of  liquid  fuel  issuing  from  the 
carburetor  nozzle,  but  this  cannot  be  done  unless  the  inlet  valve 
of  the  cylinder  opens  just  before  or  when  the  piston  reaches  upper 
dead  center  on  the  exhaust  stroke,  as  otherwise  there  will  be  no 
difference  in  pressure  between  the  inside  and  the  outside  of  the 
carburetor  and  no  suction  will  result.  Nor  will  the  admission  of  a 
charge  to  the  cylinder  be  effective  unless  the  inlet  valve  closes 
when  the  piston  reaches  or  just  after  it  passes  lower  dead  center 
on  the  upward  stroke  as  otherwise,  instead  of  being  compressed  ready 
for  firing,  the  fuel  mixture  would  again  be  forced  out  of  the  cylinder. 

Ignition  System.  Movement  will  naturally  cease  after  the 
admission  of  a  charge  unless  the  electric  spark  takes  place  at  the 
proper  moment  to  fire  that  charge  in  order  to  produce  the  power, 
or  third,  stroke  of  the  cycle.  The  entire  failure  of  the  spark  will 
prevent  further  operation;  its  occurrence  too  early  will  stop  the 
engine  by  driving  the  piston  down  in  the  reverse  direction  before 
it  has  completed  its  stroke  on  compression;  and  its  occurrence  too 
late  will  cause  a  substantial  proportion  of  the  power  to  be  wasted 
although  the  motor  will  continue  to  operate.  After  the  completion 
of  the  power  stroke  the  mechanical  system  again  enters  since, 
unless  the  exhaust  valve  opens  near  the  end  of  this  stroke,  the 
burned  gases  will  remain  in  the  cylinder  and  when  the  inlet  valve 
opens,  they  will  be  blown  back  through  the  carburetor  owing  to 
the  terminal  pressure  of  40  to  50  pounds  per  square  inch  remain- 
ing in  the  cylinder  at  the  end  of  the  power  stroke  just  before  the 
exhaust  valve  opens.  Owing  to  the  high  temperature  of  these 
gases  they  may  ignite  the  liquid  fuel  in  the  carburetor  if  blown 
back  through  it.  This  is  known  as  a  back  fire,  and  while  failure 
of  the  exhaust  valve  to  operate  is  not  as  common  a  cause  as  either 
too  lean  or  too  rich  a  mixture,  it  is  evident  that  back  fire  must 
invariably  follow  unless  the  exhaust  valve  does  open. 

Summary  of  Operation.  Continued  movement  of  the  mechani- 
cal parts  of  the  motor  is  dependent  upon  the  working  of  the  lubri- 


GASOLINE  TRACTORS  17 

eating  system.  Lubrication  fails  unless  the  cooling  system  does  its 
part  to  keep  the  temperature  down  to  a  point  where  the  move- 
ment of  the  parts  in  contact  is  possible,  as  otherwise  the  oil  is 
burned.  Unless  the  inlet  valve  opens  at  the  right  time,  the  car- 
buretor cannot  supply  a  fuel  mixture  to  the  cylinder,  while  a 
failure  of  the  electric  spark  to  ignite  this  mixture  at  the  proper 
moment  renders  the  admission  of  the  fuel  supply  useless.  Failure 
of  the  exhaust  valve  to  permit  the  escape  of  the  burned  gases 
from  the  cylinder  stops  further  operation  by  preventing  the  admis- 
sion of  a  fresh  charge. 

Value  of  Skilled  Operator.  It  is  necessary  to  take  up  each  of 
these  systems  in  detail  and  learn  the  principles  upon  which  its 
operation  is  based  in  order  to  understand  more  clearly  the  manner 
in  which  they  must  co-operate  to  produce  satisfactory  running  of 
the  engine  and  also  in  order  to  recognize  the  symptoms  at  once 
when  anything  goes  wrong  and  to  know  the  remedy  to  apply  to 
keep  the  engine  going  and  avoid  laying  up  the  machine  at  the 
time  when  it  is  most  needed.  In  the  numerous  investigations 
undertaken  by  the  Department  of  Agriculture,  some  of  which 
have  been  referred  to,  it  was  brought  out  in  a  most  striking  man- 
ner that  in  the  majority  of  cases  where  repair  bills  were  lowest 
and  the  most  satisfactory  service  was  obtained  from  the  tractor, 
it  was  due  in  very  large  measure  to  the  fact  that  a  skilled 
operator  was  on  the  job. 

It  has  not  been  a  very  uncommon  thing  in  the  past  for  manu- 
facturers to  advertise  that  their  machines  can  be  driven  by  a  child. 
So  can  a  big  mogul  freight  locomotive  be  run  by  any  boy  with 
strength  enough  to  pull  the  throttle,  but  no  railroad  company 
would '  entrust  valuable  machinery  to  the  care  of  a  boy  even  were 
the  danger  of  collision  entirely  absent.  A  tractor  cannot  be  run 
satisfactorily  by  a  boy  or  a  girl,  nor  can  it  be  so  run  by  a  man 
unless  he  takes  the  trouble  to  acquaint  himself  with  its  principles 
of  operation  instead  of  trusting  to  luck  and  experience  to  acquire 
the  necessary  information  haphazard.  In  other  words,  he  must 
qualify  as  a  skilled  operative  by  familiarizing  himself  thoroughly 
with  the  sequence  of  operations  responsible  for  the  working  of 
the  motor  and  the  principles  upon  which  those  »  operations  are 
based. 


18  GASOLINE   TH ACTORS 

VALVES   AND    VALVE   TIMING 

Placing  of  Valves.  By  referring  to  the  description  of  the  four- 
cycle method  of  operation,  it  will  be  seen  that  it  is  necessary  to 
draw  a  fuel  charge  into  the  cylinder  on  one  stroke,  compress  it  on 
the  second  stroke,  .fire  it  on  the  third,  and  exhaust  the  burned 
gases  on  the  fourth  to  complete  the  cycle.  There  must  accordingly 
be  valves  to  control  the  entrance  and  escape  of  the  gases,  and 
these  valves  must  open  and  close  at  certain  intervals  with  relation 
to  the  rest  of  the  cycle.  The  placing  of  these  valves  depends  upon 
the  type  of  motor,  of  which  there  are  three  in  general  use,  namely: 
the  L-head  motor,  in  which  the  valves  are  all  on  one  side;  the 
T-head  motor,  in  which  the  inlet  valves  are  placed  on  one  side  and 
the  exhaust  on  the  opposite  side;  and  the  valve-in-head  type,  in 
which  the  valves  are  located  directly  in  the  cylinder  heads. 

Valves  in  L-Head  Motor.  The  L-head  motor  forming  the 
power  plant  of  the  Fordson  tractor  is  shown  in  Fig.  5  in  phantom 
to  bring  out  the  details  of  the  valves  and  valve-operating  gear. 
In  a  motor  of  this  type  all  the  valves  are  placed  on  the  same  .side 
of  the  motor  so  that  in  the  line  of  eight  valves  an  inlet  and  an 
exhaust  alternate.  The  operation  of  the  valves  may  be  traced 
through  their  entire  range  of  movement  in  this  illustration  by 
noting  their  positions  in  the  different  cylinders.  Cylinder  2,  for 
example,  is  on  the  first  stroke  of  the  cycle,  the  intake  stroke. 
The  inlet  valve  is  accordingly  open  and  the  exhaust  valve  closed. 
Cylinder  1  is  shown  on  the  compression  stroke,  during  which  both 
valves  remain  closed.  This  is  also  true  of  the  explosion  stroke,  as 
indicated  by  cylinder  :>.  On  the  fourth  stroke  of  the  cycle  the 
exhaust  valve  opens  to  discharge  the  burned  gases  into  the  air,  as 
shown  by  cylinder  4.  (The  cylinder  numbers  mentioned  hen- 
refer  to  the  cylinders  counting  from  the  forward  end  and  not  to 
the  numerals  shown  on  the  illustration.) 

Valve  Details.  The  valves  used  on  automobile  and  tractor 
motors  are  variously  referred  to  as  niHxhrnuni  and  jx>i>}><'f  valves, 
the  former  name  referring  to  their  shape  and  the  latter  to  their 
method  of  operation.  The  valve  proper  counts  of  a  head  and  a 
stem,  and  as  the  valve  is  subjected  to  high  temperatures,  it  is 
either  made  of  cast  iron  welded  to  a  steel  stem  or  i>  a  piece  of 
nickel  steel  or  other  heat-resisting  metal.  Inless  some  expedient 


GASOLINE   TRACTORS  19 

of  this  nature  is  employed,  the  valve  heads  are  apt  to  warp  under 
the  terrific  heat,  this  being  particularly  true  of  the  exhaust  valves. 
The  stem  passes  down  through  a  guide  drilled  and  reamed  in  the 
cylinder  casting  itself,  and  below  the  point  where  it  leaves  this 
guide  the  stem  is  surrounded  by  a  heavy  helical  spring.  This 
spring  is  held  against  the  guide  at  its  upper  end  and  against  a 
washer  at  its  lower  end.  A  key  passing  through  a  slot  in  the  valve 
stem  itself  holds  this  washer  in  place.  The  valve  is  accordingly 
held  down  on  its  seat  by  a  strong  spring,  and  it  is  the  pull  of  this 
spring  that  returns  it  to  its  seat  with  a  snap,  or  pop,  after  it  has 
been  opened.  The  inch  or  so  of  the  valve  stem  extending  below 
the  spring  washer  contacts  with  the  valve  push  rod  when  the  latter 
is  lifting  the  valve  off  its  seat,  but  in  order  that  the  valve  may 
come  down  squarely  on  its  seat  when  closing,  the  valve  stem 
and  push  rod  should  not  be  in  contact  normally.  This  distance, 
or  clearance,  that  must  exist  between  the  valve  stem  and  the 
valve  push  rod  is  not  indicated  in  the  illustration  since,  in  this 
case,  the  valve  push  rod  also  acts  to  a -certain  extent  as  a  lower 
guide,  the  valve  stem  entering  its  upper  end  for  a  short  distance. 

Camshaft  and  Timing  Gear.  At  its  lower  end  the  valve  push 
rod  rides  on  a  cam,  and  the  position  of  this  cam  with  relation  to 
the  camshaft  determines  the  point  at  which  the  valve  will  open 
and  close.  There  is,  of  course,  a  cam  for  each  valve,  and  as  their 
positions  must  remain  absolutely  fixed,  they  are  usually  drop- 
forged  in  one  piece  with  the  camshaft  itself.  While  Fig.  5  shows 
all  the  details  of  the  valves  and  valve  gear  of  an  L-head  motor,  it 
must  be  borne  in  mind  that  every  manufacturer  has  his  own 
designs  and  standards.  For  example,  in  most  motors  a  cam  fol- 
lower is  introduced  between  the  valve  push  rod  and  the  cam  in 
order  to  minimize  the  friction.  This  usually  takes  the  form  of  a 
fork  which  is  in  a  guide  of  its  own  and  has  at  its  lower  end  a 
roller  which  rides  on  the  face  of  the  cam. 

The  inner  end  of  the  camshaft  carries  a  gear  known  as  the 
timing  gear  in  that  its  position  with  relation  to  the  smaller  gear 
on  the  crankshaft,  from  which  it  is  driven,  determines  the  time  at 
which  all  the  valves  open  and  close.  In.  a  T-head  motor  there  -are 
two  camshafts  and  two  timing  gears,  and  there  are  also  usually 
additional  gears  for  driving  the  circulating  pump  and  the  magneto, 


20 


GASOLINE  TRACTORS 


GASOLINE  TRACTORS  21 

which  make  the  timing-gear  end  of  the  average  motor  look  very 
complicated  to  the  layman.  In  the  motor  shown  in  Fig.  5  there  is 
but  a  single  timing  gear,  and  it  also  carries  the  ignition  timing 
cam  which  determines  the  occurrence  of  the  ignition  spark  in  the 
different  cylinders.  This  is  marked  Comm.  Roller  on  the  illustra- 
tion. Just  below  the  timing  cam  will  also  be  noted  zero  marks  on 
the  time  gears;  these  are  check  marks  to  enable  the  gears  to  be 
reassembled  in  the  proper  relation  after  a  motor  has  been  taken 
down  for  repairs.  The  gear  on  the  crankshaft  is  but  half  the  size 
of  the  camshaft  gear  since  each  cylinder  has  but  one  power  stroke 
for  every  two  revolutions.  There  are  two  power  strokes  per 
revolution  in  a  four-cylinder  motor,  and  the  camshaft  must 
accordingly  be  driven  at  half  the  speed  of  the  crankshaft  in  such  a 
motor. 

Timing  Valves.  In  a  motor  making  1000  r.p.m.  (revolutions 
per  minute),  2000  strokes  or  reciprocating  mqvements  of  the 
pistons  must  take  place  in  sixty  seconds,  so  that  the  entire  time 
consumed  in  making  each  stroke  at  this  speed  is  three-hundredths 
second.  A  full  realization  of  what  an  exceedingly  short  period 
this  is  in  which  to  perform  any  mechanical  operation  should  make 
it  unnecessary  to  emphasize  either  the  need  for  accurately  timed 
valves  to  ensure  an  efficient  running  motor  or  the  necessity  of 
closely  watching  all  parts  of  the  valve  gear  to  take  up  any  lost 
motion  caused  by  wear,  since  very  little  slack  is  required  to  cut 
down  the  effective  opening  of  the  valve.  For  example,  assume 
the  maximum  lift  of  the  valve  from  its  seat  to  be  J  inch  plus  the 
clearance  of  ^V  inch  provided  between  the  valve  stem  and  the 
tappet  to  permit  the  valve  to  seat  positively.  Then  if  wear  or 
lack  of  adjustment  be  permitted  to  increase  this  clearance  to  y^ 
inch,  the  valve  can  only  lift  A  inch,  so  that  the  effective  opening 
is  reduced  12 J  per  cent  for  every  thirty-second  of  an  inch  lost 
motion  between  the  valve  tappet  and  the  valve  stem. 

It  is  nothing  unusual  to  see  automobiles  brought  to  the 
repair  shop  with  so  much  clearance  between  their  valve  tappets 
and  stems  tha,t  the  valves  barely  leave  their  seats  when  the  cams 
come  around.  A  tractor  motor  would  not  be  of  much  service  in 
this  condition  since  it  would  not  develop  enough  power  to  carry 
its  load.  If  it  were  not  for  the  fact  that  usually  in  driving  an 


22  GASOLINE  TRACTORS 

automobile  only  a  very  small  fraction  of  its  power  is  used  it 
would  be  impossible  to  keep  a  motor  running  after  it  gets  in  such 
a  condition.  A  knowledge  of  the  principles  of  automobile  opera- 
tion will  be  an  aid  to  the  tractor  operator  but  he  will  do  well  not 
to  attempt  to  apply  them  literally  to  tractor  handling  since  they 
fall  far  short  of  what  is  needed  to  keep  a  tractor  running. 

In  designing  a  motor,  both  the  contour,  or  outline,  to  be 
given  the  cams  and  their  position  on  the  camshaft  are  fixed,  and 
the  finished  camshaft  is  a  single  piece  of  steel  the  cam  faces  of 
which  have  been  ground  to  a  high  degree  of  precision.  In  timing 
a  motor,  it  is  accordingly  only  necessary  to  time  the  valves  of 
one  cylinder  as  the  others  must  of  necessity  also  be  correct.  This 
process  is  made  very  simple  on  the  Ford  son  motor,  since  it  is 
accomplished  merely  by  the  correct  meshing  of  the  timing  gears. 
\Yhen  the  two  zero  marks  on  the  driving  and  the  driven  gear 
coincide  the  camshaft  is  in  the  proper  position  to  open  the  valves 
of  all  the  cylinders  in  the  correct  order.  This,  of  course,  has 
nothing  to  do  with  the  proper  adjustment  of  the  tappet  clearance, 
which  must  be  looked  after  at  each  valve. 

Check!  tiff  I'ahe  Timing.  A  closer  check  is  usually  considered 
necessary  than  is  afforded  by  the  meshing  of  the  timing  gears 
just  mentioned,  and  to  provide  this,  the  necessary  data  is  marked 
on  the  flywheel  of  the  motor  while  a  reference  point  is  also  marked 
on  the  crankcase,  Fig.  6.  In  the  illustration,  the  line  U.I).(1.  1 
and  4  shown  on  the  rim  of  the  flywheel  opposite  the  reference 
mrka  on  the  crankcase  indicates  that  that  point  represents  upper 
dead  center  for  the  pistons  of  cylinders  1  and  4.  The  line  1-1.0. 
2  and  J  indicates  that  when  that  line  on  the  rim  coincides  with 
the  reference  mark,  the  exhaust  valves  of  cylinders  2  and  X  open. 
Similarly,  /•,'/'.  /  and  4  and  1.0.  1  and  4  represent,  respectively, 
the  exhaust  closing  and  inlet  opening  points  of  cylinders  1  and  4, 
while  I.C.  2  and  .1  gives  the  inlet,  closing  point  for  cylinders  1'  and  :>. 
The  rest  of  the  points  for  the  various  cylinders  are  not  shown. 

Lead  and  Lag  of  Valve  Movement.  While  the  strong  spring 
brings  the  valve  down  on  its  seat  with  a  snap  the  moment  the 
valve  tappet  rides  oil'  the  cam,  the  valve  cannot  be  opened  in 
this  manner.  It  must  be  lifted  against  the  force  of  the  spring, 
and  as  the  time  available  for  both  its  lifting  and  its  closing  again 


GASOLINE  TRACTORS 


23 


E.Q2JM3 


is  so  very  short,  it  must  begin  to  open  somewhat  before  the 
moment  when  it  is  to  be  fully  open.  This  lead  is  given  to  the 
inlet  valves  to  a  degree  dependent  upon  the  speed  of  the  motor  in 
order  that  a  full  charge  of  fuel  mixture  may  be  drawn  into  the 
cylinder  on  the  intake  stroke. 

It  is  possible  to  start  the  opening  of  the  inlet  valve  on  the 
suction  stroke  before  the  exhaust  valve  has  closed  because  of  the 
fact  that  a  gas,  as  well  as .  a  solid  body,  has  inertia.  Inertia  is 
that  property  of  all  matter 
that  tends  to  resist  a  change 
of  state,  whether  that  state 
be  rest  or  movement.  If  a 
man  runs  full  speed  down 
a  hallway  and  a  door  at 
the  other  end  is  suddenly 
closed,  he  crashes  into  the 
door  because  he  cannot 
overcome  his  own  inertia 
in  time  to  stop.  On  the 
other  hand,  if,  when  stand- 
ing quietly  at  the  roadside, 
he  attempts  to  board  an 
automobile  passing  at 
twenty  miles  an  hour  simply 
by  grasping  the  part  nearest 
to  him,  the  consequences 
are  apt  to  be  extremely 
unpleasant  if  his  hold  is 
good.  If  it  is  not  good, 
he  stays  pretty  much  in  the  same  place  although  his  arm  gets 
a  severe  wrench.  In  the  same  manner  a  gas  possesses  inertia, 
varying  with  its  weight  and  velocity,  or  lack  of  it. 

When  the  gas  is  flowing  out  through  the  exhaust  valve  at  a 
high  rate  of  speed,  since  it  has  had  almost  the  entire  exhaust 
stroke  in  which  to  accelerate,  the  opening  of  the  intake  valve 
has  no  effect  on  its  movement.  Nor  is  there  any  risk  of  the 
incoming  fresh  charge  passing  through  the  cylinder  and  out  the 
exhaust  valve  because  its  inertia  -makes  it  as  hard  to  start  as 


E.G. 

I.O.   1  AND  4 


f.C.  2  AND  3 


\£.  (I.     ^Reference  Marks  for  Valve  Timing 


24  GASOLINE  TRACTORS 

the  high-speed  exhaust  is  to  stop  and  it  cannot  attain  any  speed 
until  the  piston  is  well  down  on  the  suction  stroke.  Then  it  in  turn 
is  hard  to  stop,  so  that  it  is  possible  to  hold  the  inlet  valve  open 
after  the  piston  has  actually  passed  the  lower  dead  center  and 
started  upward  on  the  compression  stroke.  This  delay  is  termed 
the  lag  given  the  valve  closing,  and  in  the  case  of  the  inlet  valve 
it  insures  filling  the  cylinder  with  the  fresh  charge  to  the  maxi- 
mum extent  as  the  fresh  gas  is  rushing  in  at  its  highest  speed  just 
at  that  moment;  and  every  fraction  of  a  second,  or  of  an  inch  on 
the  stroke,  that  the  valve  can  be  kept  open,  the  more  efficient 
the  motor  will  be. 

Need  of  Closely  Checking  Valves.  \Yhile  not  of  the  high- 
speed type  as  compared  with  automobile  motors,  which  run  up  to 
2000  r.p.m.  or  over,  many  tractor  motors  are  high-speed  types  for 
the  service  they  are  designed  to  render  since  the  tractor  runs  at  a 
very  considerable  fraction  of  its  load  most  of  the  time  it  is  work- 
ing while  the  automobile  motor  seldom  carries  over  20  per  cent  of 
its  full  load  and  then  only  for  very  brief  periods.  Many  tractor 
motors  are  designed  to  deliver  their  rated  output  at  1000  r.p.m., 
and  that  is  high  speed  for  a  motor  which  must  carry  80  per  cent 
of  its  maximum  load  for  eight  to  ten  hours  a  day.  Wear  of  small 
parts  such  as  valve  tappets  is  apt  to  be  rapid  in  such  service,  so 
that  to  keep  such  a  motor  up  to  a  good  degree  of  efficiency,  the 
valve  timing  must  be  carefully  checked  and  valve  tappet  clear- 
ances adjusted  to  ^V  inch  at  fairly  frequent  intervals.  This  i^ 
about  the  thickness  of  a  visiting  card.  Some  manufacturers  sup- 
ply a  small  metal  gage  for  the  purpose  of  testing  this  clearance, 
and  it  should  be  used  often  since  under  the  continued  vibration 
and  jolting  of  a  tractor  adjustments  are  apt  to  shake  loose. 

Sixteen=Valve  Engine.  Particular  attention  has  been  called 
to  the  important  influence  that  the  rapid  filling  and  emptying  of 
the  cylinders  has  on  the  efficiency  of  the  motor,  and  mention  has 
been  made  of  the  different  expedients  resorted  to  in  order  to 
increase  this.  The  limit  of  efficiency  in  this  respect  is  reached 
when  single  valves  are  used  for  the  intake  and  the  exhaust  by 
placing  both  these  valves  directly  in  the  cylinder  head,  so  that 
neither  the  incoming  nor  the  escaping  gases  have  to  go  round  any 
bends  in  entering  or  leaving  the  cylinder,  while  the  combustion 


GASOLINE   TRACTORS  25 

chamber  of  the  latter  is  entirely  free  of  pockets  or  dead  spaces. 
To  increase  the  efficiency  still  further,  multiple  valves  are  used, 
with  the  result  that  a  larger  effective  area  of  opening  is  obtainable 
with  a  given  cylinder  head  than  could  be  secured  by  increasing 
the  diameter  of  the  single  valves  to  the  maximum  permitted  by 
that  of  the  head.  In  other  words,  four  valves  are  placed  in  the 
head  with  their  centers  located  at  the  corners  of  a  square,  so  that 
the  greatest  possible  amount  of  space  available  in  the  circle  repre- 
sented by  the  combustion  chamber  is  utilized  for  valve  openings. 
Two  of  these  valves  are  used  for  the  intake,  while  the  other  two 
are  employed  for  the  exhaust. 

Twin  City  Multiple- Valve  Engine.  In  Fig.  7,  which  illustrates 
the  Twin  City  tractor  engine,  the  application  of  multiple  valves 
to  a  valve-in-head  type  of  motor  is  clearly  shown.  These  valves 
have  a  clear  diameter  of  1J  inches  and  are  operated  by  overhead 
rocker  arms,  each  arm  carrying  two  valves.  The  part  sectional 
view  at  the  left  shows  the  intake  side  of  the  motor,  while  the  end 
sectional  view  at  the  right  illustrates  the  complete  valve  operating 
gear  of  both  the  intake  and  the  exhaust  valves. 

Another  unusual  feature  of  this  engine  is  the  use  of  cylinder 
liners.  The  upper  half  of  the  crankcase  and  the  cylinders  them- 
selves are  cast  in  a  single  block.  The  liner  is  made  with  a  flange 
which  rests  on  a  ground  seat  in  the  cylinder,  so  that  when  the 
liner  is  inserted,  the  upper  face  of  the  flange  is  flush  with  the 
upper  surface  of  the  cylinder  casting  and  the  cylinder  head,  when 
bolted  on,  holds  it  in  place.  This  construction  is  clearly  shown 
in  the  right-hand  cylinder  in  the  side  elevation.  These  liners 
form  the  entire  cylinder  wall,  so  that  the  pistons  do  not  come  in 
contact  with  the  cylinder  castings  at  any  point.  The  dimensions 
of  this  motor  are  4J  by  6  inches,  and  it  is  governed  to  run  at 
1000  r.p.m.,  at  which  speed  it  is  rated  at  20  hp. 

FUEL   SUPPLY   SYSTEM 

Operating  Principle  of  Internal=Combustion  Motor.  The  prin- 
ciple upon  which  the  internal-combustion  motor  works  is  that  of 
utilizing  the  great  expansion  of  a  volume  of  hydrocarbon  vapor 
ignited  when  in  intimate  contact  with  a  sufficient  volume  of 
oxygen  to  permit  of  extremely  rapid  combustion.  In  other  words, 


26 


GASOLINE  TRACTORS 


an  "explosion  of  gas,"  so  to  speak,  is  the  driving  force  back  of 
the  piston.  The  various  phases  through  which  the  gas  passes  in 
being  drawn  into  the  motor,  compressed,  fired,  expanded,  and 
exhausted  have  been  referred  to  briefly  in  connection  with  the 
description  of  the  four-cycle  method  of  operation.  Mention  has 
also  been  made  of  the  fact  that  the  carburetor,  while  not  strictly 
speaking  a  part  of  the  motor  proper,  is  a  very  important  acces- 
sory. The  purpose  of  the  present  section  is  to  make  clear  how 
the  fuel  mixture  of  gas  and  air  is  obtained  from  the  different 
liquid  fuels  employed. 


Fig.  7.     Side  and  Knd  Sectional  Views  of  Twin  C'ity  Sixtorn-Valvo  Motor 
Courtesy  of  Minneapolis  Sled  and  Machinery  Company,  Minneapolis,  Minnesota 

Fuels  Available.  While  there  are  a  number  of  liquid  hydro- 
carbons that  may  be  employed  as  fuel  in  the  motor,  owing  to 
their  cost  but  very  few  of  them  are  available  for  tractor  opera- 
tion. It  is  scarcely  necessary  to  discuss  what  may  be  done  with 
benzol,  or  alcohol,  or  any  one  of  a  number  of  other  fuels  since 
their  present  cost  is  prohibitive.  The  choice  of  a  fuel  is  limited 
to  petroleum  and  its  derivatives,  gasoline,  kerosene,  and  distillate. 
Owing  to  the  great  demand  for  gasoline  for  other  purposes  its 
cost  has  reached  a  point  where  the  difference  between  it  and 
the  cost  of  kerosene  is  more  than  sufficient  to  offset  the  disad- 
vantages of  the  latter.  Some  fanners  prefer  to  pay  the  higher 
price  for  gasoline  because  of  the  greater  ease  of  operating  the 


GASOLINE  TRACTORS  27 

motor  with  this  fuel,  but  they  are  greatly  in  the  minority,  and 
their  plowing  operations  are  generally  on  a  comparatively  small  scale. 

Petroleum  as  it  comes  from  the  ground  is  a  heavy  viscous 
liquid  combining  in  one  fluid  practically  the  entire  range  of 
hydrocarbons  (combinations  of  the  gas  hydrogen  and  carbon)  all 
the  way  from  that  compound  so  light  that  it  is  evaporated  by 
exposure  to  the  atmosphere  before  the  oil  ever  reaches  the  refinery 
to  the  heavy  residue  that  is  left  after  all  the  refining  operations 
have  been  completed  and  that  is  suitable  only  for  making  arc-light 
carbons  or  for  similar  purposes.  So  far  as  their  value  as  fuel  for 
the  internal-combustion  motor  is  concerned,  the  only  difference 
between  any  two  of  the  hydrocarbons  contained  in  petroleum  lies 
in  their  evaporation  points,  that  is,  the  temperatures  at  which 
the  different  liquids  can  be  converted  into  vapor.  The  exceedingly 
volatile  fraction  that  passes  off  into  the  air  as  an  invisible  vapor 
practically  as  soon  as  the  oil  is  exposed  to  the  atmosphere  would 
make  an  ideal  fuel ;  it  would'  hardly  be  necessary  to  have  a  carbu- 
retor in  its  present  form  in  order  to  handle  such  a  fuel.  But  this 
highly  volatile  fraction  forms  such  a  very  small  percentage  of  the 
oil  that  running  a  motor  on  it  would  be  equivalent  to  using  per- 
fumery essence  at  a  dollar  an  ounce  for  the  same  purpose. 

Products  of  Distillation.,  Up  to  within  a  few  years  ago  the 
crude  oil  as  it  came  from  the  well  was  subjected  to  a  refining 
process  which  consisted  chiefly  of  subjecting  it  to  a  gradually 
increasing  range  of  temperatures  so  that  the  oil  was  broken  up 
into  its  various  constituent  hydrocarbons,  the  latter  being  led  off 
into  separate  vessels  where  the  vapor  was  again  condensed.  For 
example,  the  first  heat  evaporated  the  naphtha,  which  was  led  off  to 
its  own  condenser;  then  followed  gasoline,  which  was  in  turn  recon- 
verted into  a  liquid  in  another  condenser  and  was  itself  followed 
by  kerosene,  light  lubricating  oil,  heavy  lubricating  oil,  and  so  on 
down  the  scale.  This  process  of  refining,  however,  produced  but 
5  to  6  per  cent  of  gasoline  from  the  Pennsylvania  and  Ohio  crude 
oil  and  so  much  less  from  the  Texas  and  California  oils  that  it 
was  hardly  worth  while  to  attempt  to  make  gasoline  in  this 
manner  from  them. 

The  great  demand  for  gasoline  led  to  the  improvement  of  the 
process  by  the  distillation  of  the  oil  under  pressure  as  well  as  at 


2s  GASOLINE  Th  \rT(>i;s 


li  temperature,  so  ll:;il  in  ;i<l<  lil  ion  lo  the  ell'eet  of  the  heat 
in  hrr.-il.ini-.  llir  heaVJ  oil  into  its  component,  ii  \v;is  al>>  jirtiuilly 
"er;irked"  I  )  v  llir  pressure  and  ;i  lnil<li  i;reater  yield  ol'  llir  lighter 
Furl  oils  ohl;iiiir.|.  Tin-  llurlon  ;nul  tlir  I  {  il  I  m;iim  ;irr  llir  two 

processes  generally  employed,  :unl   their  products  are  sometimes 

referred    lo    a-    "cracked    oils."      These    methods    produrr   a    furl    lli;il 
eoiiimonlv     paSSefl    iindri1    llir    name    of    gasoline,    hill     \vliirli,    owing 
lo    (lir    mm  Ii    I'Tcaler    proportion    of    heavier   oil    that    il     colll  ;i  ills,   is    II 
•rade      furl      roinp;irrd      \\illl  "line     ()f      Irii      years     Jlgo. 

Kerosene    is    the    next    product,    MIX!    llirn    follow    llir    various   grade-; 

of  lubricating  oil. 

Yt'ipori/ing  Pucl.  In  nrdrr  lluil  M  furl  nuiy  hr  used  in  llir 
motor,  il  must  lirsl  hr  cnnvrrtcd  inlo  ;i  v;ipor.  Tlir  rr<juirr- 
iiM-nls  of  this  pn"<  drju-nd  rnlii-rly  upon  llir  rli;ir;ir(  rr  of  tlir 
liquid  lo  hr  Imiidlcd.  In  <li<'  <"isr  of  llir  vrry  \ol;ililr  u;i-;olinr  (,f 
\\l:ir|i  ihrrr  ;ippr;irrd  l<>  hr  .-in  unlimited  supply  \\lirn  the  jiuln- 
mohile  first  :ij»pe:ired  1  \\cnl  \  -li\c  \c;ir>  :i:-;o,  il  is  only  n:>cess;iry 
lo  expos*'  il  lo  the  ;iir,  so  tlinl  ll:c  nn  iiincnl  jiry  c;ii'hui%etors 
einploycfl  on  Ihose  first  nnloinohilrs  consisted  in  hir^e  j)jirt  of  ;i 
receptacle  for  ;i  p»>ol  of  u;i>ohnr  o\cr  which  tl:c  ;iir  \\;is  di'jiwn  lo 
nirlmrrf  it.  This  :iir  picked  uj>  the  \;ipor  ri  in-  from  I  he  surface- 
of  ihe  ^iisoline  pool  nnd  \\ilh  il  formed  ;iu  e\plosi\e  mixture. 
The  mixing  jtrocrss  n;ilm-;illy  could  not  he  curried  out  \\ith  ;my 
speed.  ;ind  il  could  not  he  depended  upon  to  he  uniform  in  its 
jietioii.  (J.-isoliiu'  evidently  hepm  to  ,u'<>  down  the  sc;ile  very 
e;irl\,  since  1  he  nexl  ste|>  \\;is  to  provide  ;i  he;i\y  \\ick  or  similar 
surface  to  .urcally  incrca  -e  the  area  e\p,,sed  to  the  air  current 
\\hich  \\;is  to  he  charged  with  the  gasoline  vnpnr.  l>ut  gasoline 
(»f  any  ^radc  that  could  he  evaporated  in  this  manner  is  no\\  a 
tiling  of  the  pa  1  . 

N/'/v////w/  A'frj'.v.v*  //•//.    \\'hcn  a  liquid  is  not  sufficiently  volatile 

to  e\aporalc  \\hcn  the  sutface  of  a  jn.ol  of  it  is  exposed  to  the 
;iir,  the  lir-l  Step  in  caiiMnu;  il  to  evaporate  is  to  hreak  il  up  into 
a  larue  niiinlx-r  of  ^lohules  and  thus  vastly  increase  the  amount 
of  surl';n-e  exposed  to  the  air.  To  hrcak  a  liquid  up  in  this  man- 
ner, it  is  spravcd  hy  heini;-  foi'ced  throuuh  a  small  orifice  known 
as  a  jet,  or  iio/./le.  The  dilVerenl  types  of  carhurctor  jt'ls,  or 
no///les,  ordinarilv-  nnploved  are  illusiralcd  in  principle  hy  F; 


GASOLINE   TRACTORS  29 

The  jet  A  is  known  as  a  fixed  jet,  in  that  it  has  no  means  of 
adjustment;  B  may  be  adjusted  by  means  of  the  screw  shown 
and  is  commonly  referred  to  as  a  needle  valve.  A  valve  of  this 
type  is  generally  employed  in  the  so-called  mixers,  which  term  is 
merely  another  name  for  a  device  that  serves  the  purpose  of  the 
carburetor  but  is  lacking  in  the  refinements  of  construction  of  the 
automobile  carburetor.  Jet  C  is  simply  a  variation  of  B  in  which 
the  needle  valve  adjustment  is  made  from  above  instead  of  below, 
while  in  D  a  cone  takes  the  place  of  the  needle  but  serves  the 
same  purpose,  that  is,  so  adjusting  the  orifice  that  the  liquid  will 
be  broken  up  into  a  spray  so  fine  as  to  be  practically  a  mist. 
The  fixed  jet  A,  while  used  abroad  to  a  greater  extent  than  here, 
is  now  becoming  more  generally  used  in  this  country  on  account 
of  its  simplicity. 

The  principle  of  all  the  types  is  identical,  namely,  drawing 
the  liquid  through  a  fine  orifice,  with  or  without  a  baffle  surface 
in  the  form  of  a  needle  or  cone,  so  that  the  liquid,  being  under 
pressure,  is  sprayed  out  of  the  opening  as  a  fine  mist.  The  suc- 
tion stroke,  or  descent  of  the  piston  in  the  first  part  of  the  cycle, 
supplies  this  pressure  by  decreasing  the  pressure  in  the  cylinder 
so  that  the  atmospheric  pressure  on  the  liquid  in  the  carburetor 
forces  it  through  the  jet. 

Mi. ring  Gas  and  Air.  As  it  comes  out  of  the  jet,  or  spray 
nozzle,  the  fuel  is  in  an  intermediate  stage  between  liquid  and 
vapor.  To  convert  it  into  the  latter,  the  descending  piston  also 
draws  up  past  the  spray  nozzle  of  the  carburetor  a  supply  of  air. 
The  latter  is  given  a  whirling  motion  by  the  shape  of  the  chamber 
it  enters,  with  the  result  that  it  picks  up  the  tiny  globules  or 
drops  of  gasoline  and  breaks  them  up  further.  With  the  volatile 
gasoline  of  earlier  days  this  was  all  that  was  required  to  produce 
a  true  vapor,  but  with  the  lower  grade  fuel  now  common,  and 
particularly  with  kerosene  and  distillate,  the  addition  of  hea4: 
is  necessary.  It  is  absolutely  essential  that  the  fuel  mist  and  the 
air  be  thoroughly  mixed  for  the  double  purpose  of  converting  the 
fuel  into  a  vapor  and  of  bringing  every  particle  of  this  vapor 
into  direct  contact  with  an  equivalent  particle  of  oxygen  in  the 
air,  since  it  is  oxygen  that  makes  the  rapid  combustion  of  the 
fuel  mixture  possible. 


30 


GASOLINE  TRACTORS 


Proportion  of  Air  to  Gas.  Unless  there  is  sufficient  air,  the 
result  is  a  slow-burning,  or  over  rich,  mixture  that  produces  a 
great  deal  of  black  smoke  and  causes  the  power  of  the  engine  to 
fall  off.  It  also  causes  the  familiar  back  fire  that  is  so  startling 
to  the  beginner.  This  occurs  because  the  fuel  is  still  burning  in 
the  cylinder  when  the  inlet  valve  opens  to  admit  a  new  charge 
and  the  latter  is  ignited  and  blown  back  through  the  carburetor 
instead  of  being  taken  into  the  cylinder.  If  there  is  too  much 
air,  the  mixture  is  thin,  or  poor.  In  such  a  case  the  power  falls 
off  and  the  engine  may  miss  in  different  cylinders,  often  jumping 
from  one  to  another  in  an  erratic  manner.  A  back  fire  will  also 
occur  with  a  lean  mixture  since  it  is  likewise  slow-burning. 


\ 


II 


Fig.  8.     Types  of  Carburetor  Nozzles  or  Jets 

To  produce  an  explosive  mixture  requires  the  mixture  of 
approximately  ten  to  fourteen  parts  by  volume  of  air  to  one  of 
fuel  vapor,  the  proportions  naturally  varying  with  the  character 
of  the  fuel  itself.  But  to  produce  an  efficient  explosive  mixture 
in  a  given  engine  requires  a  carburetor  that  has  either  been  spe- 
cially designed  for  that  particular  motor  or  one  that  has  been 
adjusted  especially  with  a  view  to  meeting  the  conditions  imposed 
by  that  motor. 

The  amount  of  air  needed  for  any  given  fuel  or  for  any  motor 
also  varies  largely  with  atmospheric  conditions  at  the  time  and 
place  in  question.  It  is  solely  the  oxygen  content  of  the  air  that 
is  of  value  in  helping  to  burn  the  fuel  mixture  rapidly,  and  at 
times  the  air  is  denser  than  at  others.  The  denser  it  is,  the  more 
oxygen  it  contains  and  the  less  of  it  is  required  to  form  a  good 
explosive  mixture.  Just  after  sundown  in  spring  and  fall  the  air 
cools  oil'  very  rapidly,  and  an  automobile  engine  will  run  noticeably 


GASOLINE  TRACTORS  31 

better  at  that  time  than  in  any  other  part  of  the  day  and  for  the 
same  fuel  consumption  the  amount  of  air  used  can  be  decreased. 
The  contrary  is  true  of  high  mountain  districts  where,  owing  to 
the  altitude,  the  air  is  thinner  and  contains  considerably  less 
oxygen  per  cubic  foot  than  at  the  sea  level.  In  climbing  from  sea 
level  to  a  height  of  several  thousand  feet,  it  is  necessary  to  allow  a 
greater  proportion  of  air  to  maintain  the  given  amount  of  oxygen 
required  for  the  efficient  combustion  of  the  fuel.  A  tractor  engine 
in  Colorado  would  accordingly  require  a  great  deal  more  air  to 
operate  efficiently  than  would  one  working  in  Illinois,  the  same 
carburetor  and  the  same  fuel  being  used  in  both  cases. 

Details  of  Spraying  Process.  Since  the  difference  between  the 
pressure  in  the  interior  of  the  cylinder  when  the  piston  is  going 
down  on  the  suction  stroke  and  that  of  the  atmosphere  (14.7 
pounds  per  square  inch  at  sea,  level)  is  not  very  great  at  the 
beginning  of  the  stroke  and  as  the  time  interval  for  charging  the 
cylinder  is  very  short,  the  spraying  of  the  fuel  into  the  incoming 
air  must  begin  immediately.  This  is  accomplished  by  carrying  a 
small  supply  of  the  liquid  fuel  in  the  float  chamber  of  the  carbu- 
retor. A  typical  carburetor  float  chamber  is  illustrated  at  the  left 
of  Fig.  9,  which  shows  a  simple  form  of  carburetor  in  section. 
The  fuel  enters  from  below  through  a  needle  valve,  the  needle  of 
which  passes  through  the  hollow  copper  float.  As  the  liquid  rises 
in  this  chamber,  the  float  rises  with  it  and  in  so  doing  forces  the 
needle  down  into  its  seat  by  means  of  the  small  weighted  levers 
shown.  The  levers  are  attached  to  a  collar  on  the  spindle  of  the 
needle. 

It  will  be  noted  that  this  float  °hamber  communicates  with 
the  spray  nozzle  located  in  the  mixing  chamber  just  to  the  right  of 
it.  As  a  liquid  always  seeks  its  own  level,  the  fuel  rises  to  the 
same  height  in  the  spray  nozzle  as  it  does  in  the  float  chamber 
and  the  float  is  set  to  close  the  needle  valve  at  a  point  where 
this  fuel  level  is  normally  but  a  small  fraction  of  an  inch  below 
the  opening  of  the  nozzle.  The  liquid  is  accordingly  sprayed 
out  of  the  nozzle  under  the  influence  of  a  difference  in  pres- 
sure of  less  than  1  pound  to  the  square  inch;  that  is,  as  soon 
as  the  pressure  above  the  nozzle  due  to  the  suction  stroke  of  the 
piston  becomes  less  than  that  of  the  atmosphere  on  the  supply 


32  GASOLINE   TRACTORS 

of  fuel  in  the  float  chamber,  the  liquid  is  forced  out  of  the  small 
opening. 

This  spray,  or  mist,  is  then  carried  upward  through  the  car- 
buretor and  through  the  inlet  valve  into  the  cylinder  by  the  cur- 
rent of  air  drawn  in  at  the  opening  below  the  spray  nozzle  and 
extending  to  the  right.  Owing  to  the  peculiar  form  given  the 
chamber  surrounding  the  spray  nozzle  (known  as  a  Venturi  tube), 
a  whirling  motion  is  imparted  to  the  incoming  air  and  its  velocity 
is  increased.  The  result  is  to  mix  the  spray  and  air  more  thor- 
oughly and  to  convert  the  mixture  more  nearly  into  a  true  vapor. 

Effect  of  Increasing  Speed.  It  is  apparent  that  as  the  speed 
of  the  motor  increases,  the  suction  on  the  spray  nozzle  will  become 
greater,  and  the  interval  between  suction  strokes,  particularly  in  a 
motor  having  four  or  more  cylinders,  will  be  so  short  that  the 
spraying  action  will  be  practically  continuous.  This  tends  to  upset 
the  balance  of  the  mixture  by  causing  an  excess  of  the  fuel  spray 
so  that  the  proper  proportion  of  fuel  to  air  is  no  longer  main- 
tained and  the  power  output  of  the  motor  suffers  correspondingly. 
To  overcome  this,  means  for  supplying  additional  air  are  provided, 
usually  in  the  form  of  an  auxiliary  air  valve  designed  to  be 
operated  by  the  difference  in  pressure  between  the  inside  and  the 
outside  of  the  carburetor.  In  Fig.  9  an  auxiliary  air  valve  of  this 
kind  is  shown  in  the  upper  part  of  the  illustration.  It  consists  of 
an  opening  in  the  carburetor  body  covered  by  a  diaphragm,  or 
plate,  the  latter  normally  keeping  the  opening  closed  by  means  of 
the  spring  shown.  As  the  pressure  inside  the  carburetor  decreases 
below  a  certain  point  owing  to  the  increasing  speed  of  the  motor, 
the  atmospheric  pressure  on  this  diaphragm  overcomes  the  spring 
and  allows  an  additional  supply  of  air  to  enter  and  combine  with 
the  mixture,  which  then  passes  off,  through  the  opening  shown  at 
the  right,  to  the  intake  manifold. 

The  carburetor  shown  in  Fig.  9  is  a  single  fixed-jet  type  with  a 
simple  auxiliary  air  valve,  and  it  serves  to  illustrate  the  principles 
upon  which  practically  all  carburetors  work,  namely,  spraying  the 
liquid  fuel  in  the  form  of  a  fine  mist  into  an  incoming  current  of 
air  to  which  greater  movement  and  increased  velocity  are  imparted 
as  it  passes  the  spray  nozzle.  There  are  a  great  many  different 
types  of  carburetors  and  an  even  greater  number  of  different 


GASOLINE   TRACTORS 


33 


makes,  but  all  operate  on  these  basic  principles.  In  some  instances 
two  or  more  nozzles  are  used,  the  smaller  being  in  action  only 
while  the  motor  is  idling  and  the  larger  increasing  the  supply  of 
fuel  when  the  increased  speed  of  the  motor  brings  a  greater  pres- 


Fig.  9.     Section  of  Typical  Fixed- Jet  Carburetor 

sure  to  bear  and  causes  them  to  spray.  In  this  case  the  principle 
K  that  of  altering  the  amount  of  fuel  in  the  mixture  in  accordance 
with  the  speed,  the  air  intake  to  the  carburetor  remaining  fixed  at 
all  times,  while  in  the  single-jet  type  described  above  the  air  sup- 
ply is  increased  with  increasing  speed.  Still  other  types  increase 
both  the  fuel  and  the  air  supply,  a  needle  valve  on  the  jet  being 


34  GASOLINE   TRACTORS 

connected  with  the  auxiliary  air  valve,  as  in  the  Schebler  carbu- 
retor shown  in  Fig.  10.  The  needle  valve,  or  spray  nozzle,  is  at  E, 
and  the  needle  is  attached  to  a  bell-crank  lever,  indicated  by  the 
dotted  lines,  which  is  attached  at  its  other  end  to  the  spindle  of 
the  auxiliary  air  valve  A.  As  the  auxiliary  air  valve  opens  down- 
ward under  the  additional  suction  of  increased  motor  speed,  it 
lifts  the  needle  E  and  permits  a  greater  amount  of  fuel  to  spray 
through  the  jet  at  the  same  time  that  an  increased  supply  of  air 
enters  through  the  valve  A.  While  it  is  automatic  in  its  action, 
this  carburetor  is  also  provided  with  a  hand  control,  the  connecting 
rod  of  which  is  attached  at  B:  The  movement  of  this  adjustment 
is  limited  by  the  boss  D  coming  against  the  stop  C.  When  in  this 
position,  it  is  set  for  running  and  corresponds  to  the  mark  AIR, 
indicating  that  the  full  air  supply  is  being  given;  at  the  other  end 
the  adjustment  quadrant  is  marked  GAS.  This  adjustment  is 
used  chiefly  for  starting.  In  this  particular  carburetor  the  float, 
which  is  not  indicated  in  the  illustration,  surrounds  the  spray 
nozzle  and  consists  of  a  shellacked  cork  ring. 

Heating  Requirements.  The  process  of  converting  a  liquid 
into  a  vapor  is  one  in  which  considerable  heat  is  rapidly  absorbed 
from  the  surrounding  air,  so  that  the  temperature  of  the  resulting 
vapor  is  lowered.  With  the  highly  volatile  gasoline  used  in  early 
days  no  artificial  heat  was  necessary  to  offset  this  under  summer 
conditions,  and  the  simple  carburetors  then  in  use  were  not  pro- 
vided with  any  heating  devices.  But  when  the  car  was  run  in 
cold  weather,  it  was  nothing  unusual  for  the  carburetor  to  become 
choked  up  with  snow  and  ice  caused  by  this  refrigerating  action  of 
evaporation,  and  this  also  happened  when  aeroplanes  first  reached 
high  levels.  The  lower  the  grade  of  fuel  employed,  the  heavier  it 
is  and  the  higher  its  temperature  of  evaporation,  so  that  heat  is 
required  even  with  gasoline  fuel  nowadays.  Kerosene  cannot  be 
vaporized  unless  the  temperature  is  raised  very  considerably  above 
that  of  the  surrounding  atmosphere  even  on  a  hot  summer  day, 
since  this  fuel  is  not  at  all  volatile  and  will  not  evaporate  at  any 
ordinary  temperature. 

Gasoline.  For  a  carburetor  handling  gasoline  only  heat  is 
ordinarily  supplied  by  water-jacketing  the  mixture  chamber,  a 
small  amount  of  hot  water  from  the  cooling  system  of  the  motor 


GASOLINE   TRACTORS 


35 


being  circulated  around  this  part  of  the  carburetor.  The  water- 
jacket  space  and  connection  of  the  fixed- jet  type  of  carburetor  will 
be  noted  in  Fig.  9.  In  addition,  the  main  supply  of  air  to  the 
carburetor  is  heated  by  clamping  a  sheet-iron  box  or  "stove" 
about  the  exhaust  manifold  and  passing  the  air  over  this  heated 
surface  before  conducting  it  to  the  carburetor  through  a  flexible 
metal  tube  of  large  diameter. 

Kerosene.     While  the  arrangements  mentioned  work  efficiently 
on  the  automobile  using  gasoline  as  a  fuel,  they  would  not  prove 


Fig.  10.     Interconnected  Air  and  Fuel  Feed 
Courtesy  of  Wheeler  and  Schebler,  Indianapolis,  Indiana 

satisfactory  for  burning  kerosene.  A  very  high  temperature  is 
required  to  vaporize  kerosene  and  the  method  of  applying  it  is 
illustrated  by  the  section  of  the  Wilcox-Bennett  kerosene  carbu- 
retor, Fig.  11.  The  float  chamber  is  shown  at  the  lower  left  hand, 
while  the  mixing  chamber,  just  to  the  right  of  it,  is  equipped  with 
two  needle  valves.  The  lower  of  these  is  designed  to  admit  water, 
which  is  required  in  the  majority  of  engines  using  kerosene  as  a 
fuel.  The  kerosene  needle  valve  is  just  above  the  water  valve, 
and  it  will  be  noted  that  the  mixing  chamber  above  this  valve 
is  surrounded  by  a  cast-iron  radiator  provided  with  fins.  The 


36  GASOLINE   TRACTORS 

function  of  this  radiator  is  to  absorb  heat  from  the  air  pass- 
ing over  the  exterior  fins  and  to  radiate  it  to  the  fuel  mixture 
inside. 

The  passage  in  which  this  radiator  is  located  is  connected 
directly  with  a  damper  in  the  exhaust  outlet  of  the  motor,  so  that 
the  exhaust  gases  may  be  passed  directly  through  it  and  used  to 
warm  the  air  instead  of  merely  utilizing  some  of  the  heat  of  the 
manifold  for  this  purpose  as  is  done  in  a  gasoline  carburetor.  In 
other  words,  all  or  part  of  the  exhaust  of  the  motor  is  used  for 
heating  by  shunting  it  through  the  carburetor  instead  of  allowing 
it  .to  escape  through  the  muffler  in  the  usual  way.  The  method  of 
accomplishing  this  in  the  Wilcox-Bennett  carburetor  is  shown  in 
Fig.  12  which  also  illustrates  the  connection  of  the  air  cleaner  to 
the  carburetor.  The  details  of  the  radiator  itself  and  the  needle 
valves  are  shown  by  the  part  sectional  view,  Fig.  13,  which 
illustrates  these  essentials  of  the  carburetor  in  the  no-load  position 
at  the  left  and  in  the  full-load  position  at  the  right.  By  compar- 
ing the  sectional  views  with  the  illustration  of  the  complete  car- 
buretor, Fig.  14,  a  better  idea  of  the  relative  positions  of  its 
essential  parts  can  be  had. 

At  the  right  in  Fig.  14  there  is  a  horn-shaped  device  surround- 
ing the  exhaust  passage  and  connecting  with  the  mixing  chamber 
of  the  carburetor  just  below  the  needle  valves.  By  referring  to 
Fig.  11  or  Fig.  13  again  it  is  seen  that  the  object  of  this  device 
is  to  conduct  heated  air  to  the  mixing  chamber.  This  hot  air  is 
required  when  the  motor  is  running  slowly  or  under  light  load,  us 
this  represents  a  condition  under  which  a  kerosene  burning  motor 
will  not  ordinarily  run  satisfactorily  since  it  is  apt  to  cool  off  too 
much.  The  passage  connecting  this  hot-air  horn  to  the  mixing 
chamber  is  designed  to  be  opened  and  closed  by  a  weighted  valve, 
which  is  indicated  in  the  drawing  by  heavy  lines.  It  has  already 
been  explained  that  the  suction  of  the  motor  varies  with  its  speed 
and  increases  very  markedly  as  the  speed  of  the  motor  increases. 
At  low  speeds  the  force  of  gravity  is  more  powerful  than  that  of 
the  motor  suction,  so  that  the  weighted  valve  remains  at  the  bot- 
tom and  the  hot-air  passage  stays  open;  when  the  motor  speed 
increases  sufficiently,  the  suction  lifts  this  valve  and  holds  it  in  a 
position  to  close  the  hot-air  passage. 


GASOLINE  TRACTORS 


37 


Air  and  Fuel  Balanced.  The  Wilcox-Bennett  kerosene  carbu- 
retor is  designed  to  be  automatically  controlled  by  the  speed  of  the 
engine,  the  amount  of  fuel,  air,  and  water  admitted  being  depend- 
ent upon  the  suction,  which  varies  almost  directly  as  the  speed. 


N 


Fig.  11.     Section  of  Wilcox-Bonnott  Kerosene  Carburetor,  Shown  at  Full  Speed  Position 
Courtesy  of  VSilcox-Benneit  Carburetor  Company,  Minneapolis,  Minnesota 

It  will  be  noted  that  the  auxiliary  air  intake  and  its  valve  are  at 
the  upper  left  hand  and  also  that  this  diaphragm  valve  is  directly 
interconnected  with  the  kerosene  needle  valve  in  the  spray  nozzle. 
A  stand  pipe  is  employed  instead  of  one  of  the  conventional  forms 
of  nozzle  previously  illustrated.  The  stand  pipe  consists  of  a  tube 


38 


GASOLINE  TRACTORS 


whose  entire  circumference  is  drilled  with  a  large  number  of  fine 
holes,  through  which  the  fuel  is  drawn  instead  of  through  a  single 
opening  at  the  top.  The  lines  to  the  right  and  the  left  of  the 
kerosene  needle  in  Fig.  11  indicate  that  the  fuel  is  issuing  from 
these  openings.  In  this  illustration  are  shown  the  essential  parts  of 
the  carburetor  in  the  position  they  assume  at  full  speed :  the  dia- 
pliragm  of  the  auxiliary  air  valve  being  depressed,  so  that  there  is  a 
flow  of  cool  air  into  the  carburetor  at  this  point;  the  kerosene  needle 
valve  is  lifted  well  off  its  seat  to  supply  the  maximum  amount 


fae/  Conr?e cfion 

Wafer  Connection 

Fig.  12.      Method  of  Kmploying  Exhaust  Gases  in  Wilcox-Bcnnctt  Carburetor 
Courtesy  of  Wilcox-Bennett  Carburetor  ('<>r/ii>an//,  Minneapolis,  Minnesota 

of  fuel;  the  hot-air  intake  below  is  closed;  and  the  water  intake, 
also  governed  by  the  weighted  valve  previously  mentioned,  is  open. 
It  must  be  borne  in  mind  that  under  the  conditions  given  the 
exhaust  of  the  motor  is  at  its  maximum  both  in  volume  and  tem- 
perature, so  that  the  kerosene  mist,  immediately  after  issuing 
from  the  standpipe  and  being  whirled  into  the  radiator  chamber 
by  the  multi-bladed  fan  shown  in  Fig.  13,  is  at  once  subjected  to  a 
decree  of  heat  reaching  at  times  as  high  as  900°  F.  Since  this  is 
too  hot  for  efficient  combustion,  before  passing  into  the  cylinder, 
the  temperature  of  the  fuel  is  lowered  somewhat  by  the  addition  of 
the  volume  of  air  entering  through  the  auxiliary  air  valve.  The 
admission  of  water  and  its  admixture  with  the  fuel  vapor  in  the 
form  of  steam  serves  to  provide  additional  cooling,  the  necessity 
for  which  will  depend  upon  the  action  of  the  motor. 


GASOLINE  TRACTORS 


39 


Gasoline  and  Kerosene  Carburetor.  Since  kerosene  will  not 
vaporize  at  ordinary  temperatures,  it  is  necessary  to  use  gasoline 
for  starting,  the  motor  being  run  on  this  long  enough  to  warm  up 
sufficiently  to  permit  the  use  of  kerosene.  The  combination  gaso- 
line and  kerosene  vaporizer  used  on  the  Fordson  tractor  is  illus- 
trated in  Fig.  15.  Being  designed  especially  for  use  on  this  one 
machine,  it  has  been  made  much  more  compact  than  types  which 
must  be  adapted  to  a  number  of  different  motors.  Compactness 


Fig.  13.     Detail  of  Radiator,  Wil cox-Bennett  Carburetor 
Courtesy  of  Wilcox-Bennett  Carburetor  Company,  Minneapolis,  Minnesota 

has  been  obtained  by  combining*  the  heating  unit  directly  with  the 
exhaust  manifold,  a  shunt  valve  being  provided  to  by-pass  the  hot 
gases  as  required. 

The  kerosene  carburetor  itself  is  shown  at  the  lower  left.  It 
is  of  the  conventional  single-jet  type,  except  that  instead  of  being 
designed  to  produce  a  working  fuel  mixture  in  the  carburetor 
proper  it  is  only '  intended  to  make  a  heavy  kerosene  mist,  with 
the  result  that  only  a  small  amount  of  air  is  drawn  through  it 
from  the  primary  air  tube.  As  shown  by  the  black  arrows  inside 


40 


GASOLINE  TRACTORS 


the  small  white  tube,  Fig.  15,  this  rich  mixture  of  kerosene  and  air 
is  drawn  through  a  heating  coil  in  a  chamber  provided  for  that 
purpose  in  the  exhaust  manifold.  From  that  point  it  passes  to  a 
mixing  chamber  above  the  inlet  manifold,  in  which  it  is  diluted  to 
the  proper  consistency  by  the  addition  of  air  through  the  auxiliary 
air  valve  shown  at  the  top  of  the  illustration.  This  air  valve  is 
controlled  in  the  usual  way,  that  is,  it  varies  its  position  with  the 
speed  cf  the  motor  itself. 

Just  below  the  mixing  chamber  are  located  the  gasoline  con- 
nection and  passage,  which  are  placed  at  this  point  since  no  heat 

is  necessary  for  starting  on  gaso- 
line and  since  the  gasoline  spray 
is  converted  into  a  fuel  mixture 
in  the  same  mixing  chamber  that 
is  used  for  the  kerosene.  The 
gasoline  vaporizing  device  is 
only  in  use  for  a  minute  or  two 
when  starting,  the  gasoline  then 
being  shut  off.  While  gasoline 
is  being  used,  the  exhaust  shunt 
lever  is  moved  to  the  ON  posi- 
tion, which  permits  all  the 
exhaust  gases  to  pass  through 
the  vapor-heating  tube  and  gives 
the  maxifhum  heating  effect. 
After  the  motor  has  been  running 
on  kerosene  for  a  short  time, 
the  shunt  lever  is  adjusted  to 
suit  the  load  conditions,  the 
temperature  of  the  mixture  being 
lowered  if  the  lever  is  moved  toward  the  OFF  position.  When  it 
is  desired  to  run  any  motor  idle  on  kerosene  longer  than  momen- 
tarily, it  is  necessary  to  supply  the  maximum  amount  of  heat  and 
the  ignition  should  also  be  retarded,  as  otherwise  the  plugs  arc 
apt  to  become  badly  sooted.  No  provision  is  made  for  supplying 
water  directly  with  the  fuel  on  the  Fordson,  but  an  air  washer 
is  used  which  serves  the  same  purpose  by  moistening  the  main  air 
supply. 


Fig.  14.     Assembled  View,  Wilcox-Bennett 

Carburetor 

Courtesy  of  Wilcox-Bennett  Carburetor  Com- 
pany, Minneapolis,  Minnesota 


GASOLINE  TRACTORS  41 

Need  for  Cleaning  Air.  About  fifteen  years  ago,  when  the 
automobile  first  began  to  assume  such  a  degree  of  reliability 
where  its  ignition  and  carburetion  mechanisms  were  concerned  as 
to  permit  some  degree  of  attention  being  given  to  ailments  of 
other  parts  of  the  motor,  carbon  deposits  were  discovered  on  the 
pistons  and  in  the  combustion  chamber.  Ever  since  then  there 
has  been  a  great  deal  of  discussion  as  to  the  conditions  which 
cause  these  deposits  and  the  methods  of  preventing  them.  A 
great  deal  of  the  discussion  and  most  of  the  methods  adopted 
have  been  misguided,  if  not  entirely  futile,  since  an  analysis  of 
these  deposits  made  at  an  early  day  proved  them  to  consist  of 
road  dirt  and  grit  to  the  extent  of  65  per  cent  or  more,  the  bal- 
ance being  simply  burned  and  partly  burned  lubricating  oil,  which 
serves  as  a  binder  and  causes  the  mass  to  adhere  to  the  cylinder 
head  or  piston.  In  addition  to  giving  rise  to  these  troublesome 
carbon  deposits,  which  frequently  accumulate  to  such  an  extent 
that  they  cause  pounding  or  even  preignition,  the  fine  grit  which 
composes  a  large  part  of  the  dirt  drawn  through  the  carburetor 
also  causes  the  pistons  and  cylinders  to  wear  very  much  more 
rapidly  than  they  would  were  the  air  free  of  this  foreign  matter. 
Notwithstanding  these  discoveries,  none  of  the  numerous  remedies 
proposed  has  ever  taken  the  preventive  form  of  cleaning  the  air 
before  it  is  used. 

Tractor  Air  Conditions  Very  Bad.  There  are  several  reasons 
why  the  troubles  caused  by  dirt  in  the  air  have  not  assumed  such 
proportions  on  the  automobile  that  it  has  been  considered  neces- 
sary to  use  a  preventive.  Chief  among  these  is  the  great  improve- 
ment that  has  taken  place  in  many  thousands  of  miles  of  American 
roads,  which  have  been  made  dustless  in  recent  years.  The  general 
recourse  to  heated  air  taken  from  a  small  box,  or  stove,  placed 
around  a  part  of  the  exhaust  manifold  is  another  reason  of  equal 
importance,  since  this  prevents  the  direct  entrance  to  the  carbu- 
retor of  the  air  passing  through  the  radiator.  Before  reaching  the 
opening  of  the  hot-air  box  on  the  exhaust  manifold  it  must  pass 
around  various  curves  and  strike  different  obstructions,  which 
cause  most  of  the  heavier  particles  of  dust  to  fall.  Since  the  high 
speed  of  the  machine  permits  it  to  run  away  from  its  own  dust 
very  effectively,  it  is  only  on  very  windy  days,  when  the  atmos- 


42 


GASOLINE  TRACTORS 


phere  is  generally  dust  laden,  that  more  than  a  very  small  amount 
finds  its  way  through  the  radiator. 

None  of  these  advantages  obtain  in  the  case  of  tractor  opera- 
tion. Plowing  must  frequently  be  carried  out  under  very  dusty 
conditions,  with  the  result  that  the  entire  machine  operates  in  the 
midst  of  a  cloud  of  dust  from  which  it  cannot  escape.  Under 
such  conditions  a  large  amount  of  dust  and  grit  is  drawn  into  the 
carburetor  as  the  suction  is  very  heavy  owing  to  the  motor  operat- 
ing under  full  load  most  of  the  time.  Unless  this  intake  of  dirt  is 


Main  Air  Tube 
Starting  Shutter 
Shunt  Valve  Lever 
Primary  Air  Tube 


Air  Valve 

Air  Valve  Guide 

Gasoline  Passage' 
(Shown  in  Shut  Position) 

Gasoline  Pipe  Connection 
Vapor  Tube    Pack    Nut 

Intake  Manifold 
^  Exhaust  Manifold 


Exhaust  Shunt" Valve1 
Vapor  Tube 
Manifold  Outlet 

•  Kerosene  Pipe  Connection  I      H* Exhaust  Pipe 

•  Float  Chamber.  Drain  Plu£  \ 

Fig.  15.     Holley  Combination  Gasoline  and  Kerosene  Carburetor  as  Used  on  the  Fordson  Tractor 
Courtesy  of  Henry  Ford  and  Son,  Inc.,  Dearborn,  Michigan 

guarded  against,  wear  of  the  moving  parts  of  the  motor  becomes 
excessive. 

Since,  as  previously  mentioned,  approximately  fourteen  parts 
by  weight  of  air  to  each  part  of  liquid  fuel  are  required  to  make 
an  efficient  burning  mixture,  the  equivalent  in  volume  of  10, (MM) 
gallons  of  air  is  needed  for  every  gallon  of  fuel.  In  the  case  of  a 
tractor  burning  20  gallons  of  fuel  in  a  day's  work,  a  volume  of  air 
equal  to  200,000  gallons  must  pass  through  the  carburetor  and 
cylinders  in  ten  hours.  The  amount  of  dust  that  such  a  great 
volume  of  air  can  hold  in  suspension  under  the  conditions  of 


GASOLINE   TRACTORS  43 

tractor  operation  makes  the  importance  of  thoroughly  cleaning  the 
air  too  apparent  to  call  for  any  emphasis. 

Types  of  Air  Cleaners.  Air-Washer  Type.  It  is  apparent 
that  two  or  three  different  principles  may  be  taken  advantage  of 
to  remove  dust  and  grit  in  suspension  from  a  moving  mass  of  air. 
The  first  of  these  to  suggest  itself  is  that  of  actually  washing  the 
air  by  passing  it  through  a  body  of  water,  and  a  number  of  air 
cleaners  are  based  on  this  idea.  The  action  of  the  air  in  passing 
up  through  the  water  is  indicated  in  Fig.  16,  and  it  will  be  noted 
that  in  addition  to  dropping  its  dust  and  other  foreign  matter  the 
air  carries  with  it  quite  a  percentage  of  moisture,  so  that  the 
washing  process  is  a  further  advantage  in  those  motors  that  require 
considerable  water  to  insure  cool  running  when  burning  kerosene. 
When  using  gasoline,  however,  washing  the  air  is  apt  to  be  quite 
the  contrary  since  the  excessive  amount  of  water  tends  to  cool  the 
mixture  too  much  to  permit  efficient  operation.  The  air  washer 
employed  on  the  Fordson  tractor  is  shown  in  section  in  Fig.  17. 
'It  consists  of  a  water  tank  with  a  central  intake  tube  and  an  air 
guide  mounted  on  a  float  and  surrounding  the  intake  tube.  The 
suction  of  the  motor  serves  to  draw  air  into  the  washer,  and  it  is 
then  deflected  downward  into  the  water  by  the  air  guide.  In 
order  that  the  air  may  pass  through  a  considerable  depth  of  water, 
the  air  guide  is  attached  to  the  float  shown  so  that  the  air  will 
always  enter  the  water  at  the  same  distance  below  the  water  level. 
The  float  keeps  this  distance  constant  by  maintaining  the  outlet 
of  the  air  guide  at  the  same  point  at  all  times  regardless  of  the 
amount  of  water  in  the  bowl.  The  air  guide  mentioned  also 
serves  another  purpose  in  that  it  serves  to  cut  off  the  air  supply 
when  the  water  supply  is  allowed  to  fall  so  low  that  the  float 
rests  on  the  bottom  of  the  bowl. 

Centrifugal  Type.  Mention  has  already  been  made  of  the  fact 
that  in  compelling  the  current  of  air  drawn  'through  the  radiator 
of  an  automobile  to  pass  around  several  obstructions  most  of  the 
heavier  grit  is  allowed  to  drop  before  the  air  can  reach  the  carbu- 
retor intake.  By  purposely  giving  the  current  of  air  a  whirling 
movement  this  effect  can  be  accentuated  by  taking  advantage  of 
centrifugal  force  to  throw  the  particles  of  dust  to  the  outer  edge 
of  the  container,  where  they  drop  into  a  receptacle.  This  is  the 


44 


GASOLINE    TRACTOKS 


principle  upon  which  the  air  cleaner  shown  in  Fig.  18  is  based. 
By  referring  to  the  phantom  view  of  the  same  air  cleaner,  Fig.  19, 
it  is  seen  that  after  entering,  the  air  is  conducted  through  curved 
channels,  from  which  it  issues  to  again  strike  a  large  central  cone, 
thus  acquiring  a  whirling  motion  which  tends  to  deposit  on  the 
sides  of  the  cone  all  matter  in  suspension  that  is  heavier  than  air. 

This  matter  then  gravitates 
down  the  sides  of  the  cone  and 
finally  drops  off  the  edge  into 
the  glass  receptacle  placed 
below,  which  permits  the  oper- 
ator to  note  the  accumulation 
of  dust  and  remove  it  in  good 
season. 

The  same  principle  is 
also  employed  in  connection 
with  a  receiving  vessel,  or 
dust  collector,  containing 
water.  An  air  cleaner  of  this 
type  is  shown  in  Fig.  20,  and 
a  sectional  view  in  Fig.  21. 
In  the  latter  illustration  the 
action  of  the  air  currents  in 
entering  and  striking  the 
central  cone  is  more  clearly 
indicated  by  the  arrows.  The 
air  is  first  drawn  into  the 
outer  casing  and  the  spiral 
-  tubes  at  A.  These  tubes  are 
i-.et  on  the  inner  circumference 
of  the  casing,  so  that  the 
action  of  the  air  causes  the 
water  to  whirl  rapidly  and  assume  the  position  indicated  by  the 
dotted  line,  exactly  as  any  liquid  will  do  in  a  bowl  when  stirred  in 
one  direction  very  rapidly.  The  water,  on  striking  against  the 
lower  projecting  edges  of  the  spiral  tubes,  is  broken  up  into  a  fine 
spray  through  which  the  air  passes  in  being  cleaned.  The  washed 
air  then  rises  and  enters  the  opening  C  of  the  inner  cleaner,  where 


is.  16. 


Sectional  View  of  Parrett  Wet-Type 
Ai 


Courli  >  /   c/   1'iirritt    Trnrtnr   Company, 
Chicago 


GASOLINE   TRACTORS  45 

it  is  again  subjected  to  a  violent  whirling.  This  further  tends  to 
throw  down  any  particles  of  dust  or  water  which  may  have  been 
carried  along  with  the  air,  the  accumulation  of  dust  being  deposited 
at  the  bottom  of  the  tube  B.  In  a  short  time  enough  dirt  col- 
lects to  form  a  mud  seal  for  this  tube,  so  that  if  the  operator  for- 
gets to  renew  the  water  supply,  the  cleaner  will  continue  to 
operate  as  a  dry  type. 

Felt  Baffle  Type.  The  third  principle  available  in  cleaning  air 
is  that  of  the  dust  screen,  and  the  method  of  employing  this  is 
illustrated  in  Fig.  22,  which  shows  the  device  in  partial  section. 
It  consists  of  a  cylinder  of  wire  gauze  on  which  felt  is  stretched. 
The  air  strikes  this  in  entering,  and  the  dust  it  contains  is  repelled 
by  the  felt  while  the  air  passes  through  and  on  to  the  carburetor 
by  means  of  a  connection  with  this  inner  chamber.  The  vibration 
of  the  motor  as  well  as  the  force  of  the  current  of  air  itself  tends 
to  shake  particles  of  dust  off  the  felt  and  prevent  their  clogging  it, 
the  dust  dropping  out  through  the  holes  shown.  In  cold  weather 
these  holes  may  be  closed  to  conserve  the  heat,  and  the  dust  then 
collects  in  the  outer  chamber  until  removed  by  hand. 

Attention  Required.  Regardless  of  the  type  of  air  cleaner 
employed,  the  chief  attention  required  is  the  frequent  removal  of 
the  accumulation  of  dust,  or  mud  in  case  an  air  washer  is  used. 
Neglect  of  this  precaution  simply  makes  conditions  very  much 
worse  than  they  would  be  were  no  air  cleaner  employed,  since  the 
accumulation  of  dirt  in  the  cleaner  is  apt  to  be  drawn  directly 
into  the  motor.  Where  an  air  washer  is  employed,  the  deposit  of 
mud  is  converted  into  dust  very  quickly  by  the  heat  of  the  motor, 
though  the  partial  shutting  off  of  the  air  supply  causes  the  motor 
to  miss  and  lose  power,  thus  providing  a  warning  of  the  lack  of 
water. 

LUBRICATING    SYSTEM 

Effect  of  Temperature  and  Pressure.  Where  the  lubricating 
system  is  concerned,  as  well  as  regards  other  essentials,  the  novice 
in  tractor  operation  will  do  well  not  to  rely  on  his  automobile 
experience  to  carry  him  through  without  a  slip  that  will  result  in 
serious  damage.  There  can  be  no  comparison  whatever  between 
the  30-hp.  automobile  motor  that  runs  for  ten  hours  a  day  and  is 
seldom  called  upon  to  deliver  50  per  cent  of  its  rated  power  and 


46 


GASOLINE   TRACTORS 


GASOLINE   TRACTORS 


47 


the  tractor  engine  of  the  same  rating  that  is  delivering  80  to  85 
per  cent  of  its  rated  output  all  day  long. 

The  sole  object  of  lubrication  is  to  prevent  moving  surfaces 
from  coming  into  actual  rubbing  contact  of  metal  to  metal,  in 
other  words,  to  maintain  a  film  of  lubricant  between  the  two 
surfaces  on  which  they  may  actually 
be  said  to  float,  though  the  film 
itself  may  be  only  a  few  thou- 
sandths of  an  inch  in  thickness. 


Fig.  18.    Wilcox-Bennett  Fry-Type 

Air  Cleaner 

Courtesy  of  Wilcox-Bennett  Carbu- 
retor Company,  Minneapolis, 
Minnesota 


Fig.    19.      View    Showing    Method    of 
Separating  Dust  from  Air  by  Cen- 
trifugal Force 

Courtesy   of   Wilcox-Bennett    Carburetor 
Company,  Minneapolis,  Minnesota 


The  problem  is  accordingly  the  same  in  the  automobile  and  the 
tractor  engines,  but  the  ease  with  which  a  film  of  lubricant  may 
be  maintained  between  moving  surfaces  depends  upon  the  sur- 
rounding temperature  and  the  pressure  under  which  the  surfaces 
move  in  contact.  When  the  temperature  of  the  circulating  water 
is  seldom  allowed  to  exceed  165°  F.,  as  in  an  automobile  motor 
running  under  but  a  fraction  of  its  maximum  load,  the  vaporizing 
point  of  the  lubricating  oil  is  seldom  reached.  But  in  a  tractor 
engine  running  for  hours  at  close  to  its  full  load  the  circulating 
water  is  seldom  much  below  the  boiling  point  at  sea  level,  212°  F., 
and  the  conditions  of  operation  are  such  that  every  part  of  the 


48 


GASOLINE   TRACTORS 


engine  is  very  much  hotter  than  this.  Under  the  heavy  load  the 
pressure  between  the  piston  and  the  cylinder  wall  is  much  greater, 
and  the  oil  tends  to  squeeze  out  much  more  rapidly,  so  that  it 
must  be  renewed  with  far  greater  frequency  than  is  necessary  in 
an  automobile  engine. 

Types  of  Lubricating  Systems.  Splash  System.  The  earliest 
practical  type  of  lubricating  system  used  on  the  automobile  engine 
was  the  splash  system.  The  crankcase  is  filled  with  oil  to  a  cer- 
tain level,  and  the  big  ends  of  the  connecting  rods  dip  into  it  and 
splash  it  all  over  the  interior  of  the  motor.  To  keep  up  the  sup- 


CLE.AN  AIR 
To 

CARBURETER 


Fig.  20.   Wilcox-Bennett  Wet  Type 
Air-Cleaner 


Fig.  21.      Method  of  Operation  in  Wilcox- 

Bennett  Wet-Type  Air  Cleaner 

Courtesy  of  \Vilror-Iiennett  Carburetor  Compani 

Minneapolis,  Minnesota 


ply,  1  quart  or  more  of  oil  is  added  at  the  beginning  of  a  run, 
which  results  in  having  too  much  oil  at  the  start  and  not  enough 
at  the  finish.  Moreover  oil  is  not  always  oil  so  far  as  its  lubricat- 
ing properties  are  concerned,  since  they  are  burned  out  of  it  by 
high  temperature.  Therefore  after  a  few  days'  steady  use  the  oil 
becomes  practically  useless,  and  only  the  extra  quart  or  two  added 
to  keep  up  the  level  serves  as  lubricant. 

When  the  motor  is  run  very  cool,  either  with  gasoline  or  ker- 
osene, a  certain  proportion  of  the  fuel  mixture  is  condensed  in  the 
cylinders  and  finds  its  way  past  the  pistons  into  the  crankcase, 
thus  thinning  the  oil  out  and  further  reducing  its  lubricating 


GASOLINE   TRACTORS 


49 


value.  This  is  particularly  true  of  kerosene,  which  has  the  further 
disadvantage  under  such  conditions  of  washing  the  film  of  oil  off 
the  sides  of  the  cylinder  walls  as  it  gravitates  to  the  crankcase. 
One  instance  is  cited  in  which  a  manufacturer  agreed  to  deliver  a 
tractor  under  its  own  power,  but  after  a  few  hours  running  so 
much  kerosene  found  its  way  into  the  crankcase  that  the  main 
bearings  were  burned  out  and  the  tractor  had  to  be  towed  back  to 
the  shop  for  repairs  before  ever  reaching  its  prospective  owner. 
In  another  case .  that  illustrates  the  fallacy  of  depending  upon 
automobile  precedents  a  factory  man  was  called  to  the  assistance 
of  a  farmer  who  reported  that  the 
bearings  of  his  motor  had  burned  out 
before  the  end  of  the  first  week's  work. 
When  asked  what  he  had  done  to  lubri- 
cate the  motor,  the  farmer  said  that  he 
had  added  oil  as  often  as  he  did  on  his 
Ford. 

Modified  Splash  System.  The  simple 
splash  system  of  lubrication  is  "accord- 
ingly not  practical  on  the  tractor  engine, 
though  it  is  successfully  employed  on 
hundreds  of  thousands  of  automobile 
motors.  A  small  percentage  of  the 
tractors  now  in  use  employ  this  system 
but  as  a  rule  it  is  improved  by  the 
addition  of  some  means  of  constantly 
feeding  fresh  oil  to  the  crankcase  or 
of  circulating  it  over  the  bearings 
and  depending  only  upon  the  over- 
flow from  the  latter  to  furnish  splash  lubrication.  The  cross- 
section  of  a  Waukesha  motor,  Fig.  23,  gives  an  excellent  idea  of 
how  the  dippers  on  the  ends  of  the  connecting  rods  distribute  the 
oil  to  every  part  of  the  motor.  Large  receptacles  over  the  main 
bearings  are  kept  constantly  filled,  while  the  spray  of  oil'  thrown 
up  reaches  even  to  the  valve  stems.  The  crankcase  is  divided 
into  compartments,  as  shown  in  Fig.  24,  which  illustration  also 
shows  the  oil  pan  forming  the  bottom  of  the  crankcase.  The  oil 
is  raised  by  a  small  pump,  forced  through  the  wire  gauze  screen 


Fig.  22.     Orem  Felt-Type  Dry 
Air  Cleaner 


50 


GASOLINE  TRACTORS 


Fig.  23.     Sectional  End  View  of  Waukesha  Motor,  Showing  Operation  'uul  Interior  Construct i,,n 
Courtesy  of  Waukesha  Motor  Company,  Waukcaha,  Wisconsin 


GASOLINE  TRACTORS 


51 


S,  and  distributed  to  the  different  compartments  of  the  bleeder 
tube,  or  pipe  having  openings  A,  B,  C,  and  D.  The  overflow 
returns  to  the  pump  and  is  again  distributed,  so  that  this  is  what 


Fig.  24.     Crank  Case  Oil  Part,  Showing  Compartments  and  Bleeder  Tube 
Courtesy  of  Waukesha  Motor  Company,  Wmtkesha,  Wisconsin 


Fig.  25.     Diagram  of  Combination  Force-Feed  and  Splash  Lubrication 
Courtesy  of  J*  I.  Case  Plow  Works,  Racine,  Wisconsin 

may  be  termed  a  circulating-splash  system  of  oiling.  A  gage  on 
the  crankcase  shows  the  level  of  the  oil.  In  some  systems  of  this 
kind  the  stroke  of  the  oil  pump  is  regulated  to  feed  the  oil  slowly 
and  it  remains  in  the  crankcase  until  consumed. 


52 


GASOLINE  TRACTORS 


Force-Feed  Splash  System.  In  the  force-feed  splash  system 
reliance  is  not  placed  entirely  upon  the  splash  of  oil  in  the  crank- 
case  to  reach  all  surfaces  in  need  of  lubrication,  but  a  supply  of 
oil  is  forced  directly  to  the  main  bearings,  camshaft  bearings,  and 
timing  gears,  and  the  overflow  from  these  points  is  allowed  to  col- 
lect in  the  crankcase  and  serve  for  splash  lubrication  for  the  pistons, 
piston  pins,  connecting  rods,  and  cams.  Copper  tubes  are  usually 
placed  on  the  sides  of  the  connecting  rods  to  lead  the  oil  to  the  piston 
pins,  and  in  some  cases  this  oil  is  also  relied  upon  to  lubricate  the 


Fig.  -<>.     Molitit'  Circulating  Pressure  Force-Feed  Lubrication 

cylinder  walls,  since  it  is  forced  out  of  the  hollow  pin  on  to  the  cyl- 
inder. An  indicator  in  sight  of  the  operator  shows  whether  the 
oil  is  being  supplied  by  the  force  feed.  The  partial  section  of  the 
(  'ase  engine,  Fig.  25,  illustrates  the  details  of  a  system  of  this  type. 
Necessity  for  Discarding  Used  Oil.  One  of  the  chief  draw- 
backs to  all  forms  of  splash  systems  of  lubrication  for  the  tractor 
is  the  difficulty  of  educating  the  farmer  up  to  a  realization  of  the 
saving  that  ihe  constant  renewal  with  fresh  oil  represents  in 
repairs.  Lubricating  oil  is  the  most  expensive  single  item  of  sup- 


GASOLINE  TRACTORS 


53 


ply  for  the  tractor,  regarded  solely  from  the  standpoint  of  its  cost 
per  gallon,  and  the  farmer  dislikes  to  throw  it  away  no  matter 
how  long  it  has  been  used.  Some  tractor  manufacturers  recom- 
mend that  the  crankcase  be  drained  at  the  end  of  every  day's 
work,  washed  out,  and  refilled  with  fresh  oil.  When  oil  has  been 
used,  its  structure  is  broken  down  by  the  high  temperature.  It  is 
"cracked" — exactly  as  petroleum  is  in  the  pressure  distillation 
process  by  which  all  petroleum  fuels  are  produced  nowadays — and 
it  has  lost  its  lubricating  qualities.  By  taking  a  sample  of  oil 


Fig.  27.     Combination  Force-Feed  and  Splash  Lubrication.    Detroit  Fourteen-Lead 

Chain-Driven  Oiler 
Courtesy  of  Aultman- Taylor  Machinery  Compant/,   'Manxfu'lil,  Ohio 

that  has  been  used  in  the  crankcase  for  several,  days  and  rubbing 
it  between  the  fingers,  the  great  difference  between  it  and  a  sample 
of  fresh  oil  will  be  noted.  The  average  user  does  not  like  to 
drain  the  crankcase  every  day,  and  some  practice  the  false  econ- 
omy of  draining  it  but  once  a  season.  It  will  be  found  much 
cheaper  at  the  end  of  a  season's  work  to  have  bought  plenty  of 
good  lubricating  oil  and  used  it  but  once,  than  to  attempt  to 
economize  by  using  it  over  and  over  again.  Repairs  always  cost 
far  more  than  oil.  The  used  oil  may  be  employed  to  lubricate  other 
parts  of  some  machines,  such  as  the  track  of  a  caterpillar  tractor. 


54 


GASOLINE   TRACTORS 


Pressure-Circulated  Lubrication.  Following  automobile  prac- 
tice, some  motors  have  the  crankshaft  drilled  throughout  its 
length  and  tubes  connecting  with  this  bore  rising  from  the  con- 
necting rod  bearings,  so  that  the  pressure  generated  by  the  pump 
causes  the  oil  to  flow  over  these  bearings  constantly,  the  cylinder 
walls  being  lubricated  by  the  overflow  through  the  piston  pins. 


Fig.  28.     Force-Feed  Oiler  of  Two-Cylinder  <  Hl-PuM  Kn"ino 
Courtesy  of  Advance-  Rumcly  Thretker  Compmy,  Inc.,  /.<;/>»/•/»•, 


In  this  system  no  dependence  is  placed  on  splash  lubrication,  jt:-.d 
the  connecting-rod  big  ends  are  not  allowed  to  dip  into  the  over- 
flow, as  shown  by  the  section  of  the  Moline  motor,  Fig.  26. 

This  system  is  also  known  as  the  dry-crankcase  type  in  that 
the  excess  oil  drops  into  a  sump,  or  well,  below  the  crankcase  in 
which  the  pump  is  located,  with  the  result  that  the  entire  supply 


GASOLINE  TRACTORS  55 

is  constantly  kept  in  circulation.  More  than  one  pump  is  some- 
times employed  for  this  purpose,  so  that  oil  is  drawn  from  differ- 
ent parts  of  the  crankcase  at  the  same  time.  The  advantage  of 
this  method  is  that  the  location  of  the  machine,  as  in  climbing  a 
hill,  has  no  effect  on  the  quantity  of  lubricating  oil  that  reaches 
every  part  of  the  motor. 

Fresh-Oil  System.  A  very  considerable  percentage  of  all  the 
tractors  now  in  use  follow  steam-engine  practice  in  lubrication  by 
feeding  only  as  much  oil  as  is  required  by  each  bearing,  so  that 


Fig.  29.     Eccentric-Driven  Force-Feed  Oiler 

Courtesy  cf  II art- Parr  Company,  Charles  City,  Iowa 

the  oil  is  consumed  almost  as  fast  as  it  is  fed.  This  has  the 
advantage  of  constantly  renewing  the  lubricating  film  with  fresh 
oil.  To  provide  a  factor  of  safety,  however,  the  supply  must 
actually  be  fed  faster  than  it  is  used  by  the  bearings  in  order  that 
oil  may  accumulate  in  the  crankcase,  and  unless  this  is  drained  off 
at  frequent  intervals,  this  system  is  open  to  the  same  objection  as 
the  ordinary  splash  system. 

The  supply  of  fresh  oil  for  a  system  of  this  type  is  carried  in 
an  external  reservoir  which  also  serves  as  the  lubricator,  in  that  it 
is  fitted  with  a  number  of  small  plunger  pumps,  one  for  each  lead, 


56  GASOLINE  TRACTORS 

or  tube  leading  to  the  bearings.  The  lubricator  is  driven  by  a 
belt,  chain,  or  rod  (preferably  the  last  named)  from  the  camshaft 
of  the  motor,  as  shown  in  Fig.  27,  which  illustrates  the  Aultman- 
Tavlor  engine  equipped  with  a  fourteen-lead  Detroit  lubricator. 
Fig.  28  shows  a  similar  lubricator  on  the  Rumely  two-cylinder 
motor,  and  Fig.  29  a  Madison-Kipp  lubricator  on  the  Hart-Parr 
engine,  -an  eccentric  or  crank  an4  rod  being  employed  to  drive  the 
lubricator  pumps  in  both  instances. 

Frequent  Attention  Necessary.  On  an  automobile,  it  is  noth- 
ing unusual  for  grease  cups  to  go  an  entire  season  without  being 
refilled,  and  during  that  time  they  have  only  been  turned  down 
once  or  twice.  How  radically  different  is  the  attention  required 
by  a  tractor  may  be  appreciated  from  the  instructions  for  oiling 
an  International  tractor.  When  doing  belt  work,  the  grease  cup 
on  the  pulley  must  be  turned  down  every  hour.  There  are  eleven 
bearings  on  the  fuel  and  water  pumps,  camshaft,  front  wheels, 
rear  axle,  and  clutch  that  require  turning  down  every  two  hours 
that  the  tractor  is  running.  On  another  group  of  ten  bearings  the 
grease  cups  must  be  turned  down  twice  a  day,  while  three  others 
must  be  turned  down  once  a  day. 

COOLING   SYSTEM 

Heat  Efficiency  of  Motors.  While  the  thermal,  or  heat, 
efficiency  of  the  tractor  motor  is  high  as  compared  with  that  of  a 
steam  engine,  in  which  it  is  difficult  to  utilize  more  than  8  per 
cent  of  the  available  heat  of  the  coal,  it  is  an  unfortunate  fact 
that  a  very  large  part  of  the  heat  available  in  gasoline  or  kerosene 
must  also  be  wasted  since  no  method  that  will  utilize  more  of  it 
has  yet  been  discovered.  Considering  the  fuel  value  of  the  enter- 
ing charge  as  100,  about  40  per  cent  of  this  escapes  through  the 
exhaust  valve  at  the  end  of  the  power  stroke  and  during  the  suc- 
ceeding exhaust  stroke.  An  additional  35  per  cent  that  cannot  be 
utilized  to  drive  the  piston  by  its  expansion  must  be  absorbed  and 
quickly  dissipated  or  it  will  soon  overheat  the  motor  and  bind  the 
pistons  hard  and  fast  in  the  cylinders.  Thus  only  25  per  cent  of 
the  ival  value  of  the  fuel  is  converted  into  power.  These  are 
simply  average  percentages  which  may  be  made  poorer  or  better 
by  the  type  of  engine,  some  simple  steam  engines  working  in  the 


GASOLINE   TRACTORS 


57 


open  in  cold  weather  and  poorly  protected  not  showing  an  effi- 
ciency to  exceed  3  or  4  per  cent,  while  a  condensing  Corliss  type 


unit  would  reach  17  per  cent  and  a  modern  type  Diesel  oil  engine 
35  per  cent  or  better. 

Types  of  Cooling  Circulation.    To  carry  the  great  amount  of 
excess  heat  away  from  the  cylinder  heads  and  exhaust  valve  ports 


58  GASOLINE  TRACTORS 

with  sufficient  rapidity  to  prevent  these  parts  becoming  over- 
heated, a  body  of  cool  water  is  kept  in  direct  contact  with  them 
and  is  replaced  by  fresh  water  as  quickly  as  it  can  absorb  the  heat. 
This  water  is  contained  in  the  jackets — spaces  cast  in  the  cylinder 
walls  and  cylinder  head  for  this  purpose.  The  cool  water  is  con- 
ducted to  the  lowest  part  of  this  water-jacket,  passed  up  over  the 
hottest  parts  of  the  cylinder,  and  then  led  to  the  radiator  consisting 
of  a  bank  or  nest  of  tubes.  These  tubes  are  made  of  copper, 
which  is  an  excellent  conductor  of  heat  as  well  as  of  electricity, 
and  their  cooling  surface  is  greatly  increased  by  surrounding  them 
with  thin  copper  fins  which  give  up  their  heat  to  the  air  very 
readily.  The  movement  of  the  water  between  the  jackets  and  the 
radiator  is  termed  the  cooling  circulation. 

Thermo-Syphon  Circulation.  The  circulation  of  the  water  may 
be  effected  by  the  difference  in  the  temperature  of  the  water  itself 
or  may  be  brought  about  by  forcing  the  water  through  the  piping 
at  high  speed  by  a  pump.  The  first  method  is  known  as  thermo- 
syphon  circulation  and  its  operation  is  illustrated  by  the  view  of 
the  cooling  system  of  the  Fordson  tractor,  Fig.  30.  The  radiator 
is  shown  in  section,  while  the  flow  of  water  through  the  connecting 
pipes  and  the  cylinder  jackets  and  head  is  indicated  by  the  arrows. 
After  passing  downward  through  the  radiator,  the  water  issuing 
at  the  bottom  is  considerably  cooler  than  that  at  the  top  of  the 
cylinder  jackets,  which  has  been  absorbing  its  charge  of  heat.  As 
water  gets  hotter,  it  expands  and  becomes  lighter,  so  that  it  tends 
to  rise.  The  water  in  the  cylinder  head  jacket  accordingly  flows 
toward  the  radiator  and  is  replaced  by  fresh  water  rising  through 
the  cylinder  jackets.  The  hotter  the  water  gets,  the  faster  it 
(lows,  its  movement  being  controlled  entirely  by  the  difference  in 
temperature  between  the  water  entering  and  the  water  leaving  the 
system  at  the  coolest  and  hottest  points.  It  will  be  noted  in  the 
illustration  how  sliort  and  direct  the  connections  are  and  how 
large  their  diameter  is  as  compared  with  the  connections  on  a 
motor  on  which  a  pump  is  employed  to  provide  forced  circulation 
of  the  cooling  water,  Fig.  31. 

Forced  Circulation.  On  the  majority  of  tractors  a  forced  type 
of  circulation  is  employed.  In  this  type  the  water  is  moved  around 
through  the  cylinder  jackets  and  to  the  radiator  and  back  by 


GASOLINE  TRACTORS  59 

means  of  a  centrifugal  pump  driven  from  the  camshaft  or  one  of 
the  other  auxiliary  shafts  of  the  motor.  The  body  of  water  car- 
ried, the  size  of  the  cylinder  jackets,  and  the  diameter  of  the  con- 
necting pipes  may  all  be  made  much  smaller  than  in  systems 
where  the  water  must  move  under  the  force  of  its  own  difference 
in  temperature,  as  in  the  therm o-syphon  system.  But  it  is  also 
apparent  that  the  factor  of  safety  is  also  somewhat  lower  in  the 
forced  circulation  type  than  in  the  other.  Any  failure  of  the  pump, 
fan,  connections,  or  radiator  must  be  detected  and  the  engine 


Fig.  31.     Pump  and  Connections  of  Forced-Circulation  Cooling  System  Used 

on  Heider  Tractor  Engine 
Courtesy  of  Rock  Island  Plow  Company,  Rock  Island,  Illinois 

stopped  at  once  if  serious  damage  is  to  be  avoided.  With  an 
engine  that  is  designed  to  be  run  constantly  under  such  a  high 
percentage  of  its  maximum  load  for  a  number  of  hours  as  the 
tractor  engine,  the  cooling  and  lubricating  systems  are  of  the 
greatest  importance.  This  is  true  particularly  of  the  cooling  sys- 
tem since  any  failure  in  it  involves  the  lubrication  system  as  well, 
as  the  moment  the  temperature  rises  beyond  control,  the  lubricating 
oil  is  burned  to  carbon  and  the  damage  is  done. 

Protection  of  Radiator  from  Stresses.    The  tubular  type  of 
radiator  is  the  most  practical  for  tractor  use  owing  to  the  neces- 


GO  GASOLIXK   TRACTORS 

sity  for  withstanding  constant  vibration  and  also  jolting  and  rack- 
ing, and 'it  is  good  practice  to  support  the  radiator  on  a  flexible 
mounting  so  that  these  stresses  cannot  affect  it  directly.  This 
refers  particularly  to  the  straining  and  racking  due  to  the  pas- 
sage of  the  tractor  over  very  uneven  surfaces.  To  prevent  damage 
from  this  cause,  some  radiators  are  mounted  on  a  pin  and  trun- 
nion, others  have  a  three-point  support,  while  still  others  are 
located  at  points  on  the  frame  where  they  will  be  subjected  to  the 
least  stress  from  the  twisting  and  bending  due  to  rough  going. 
In  the  illustrations  in  the  section  on  motors  the  pumps  and  con- 
nections used  on  some  of  the  machines  are  noticeable  so  that  it  is 
unnecessary  to  illustrate  them  here. 

Automobile  Experience  Misleading.  When  first  undertaking 
the  management  of  a  tractor,  the  average  operator  is  very  apt  to 
be  guided  by  his  automobile  experience  and  treat  the  heavier  and 
slower-traveling  machine  in  the  same  manner.  This  is  apt  to  lead 
to  serious  errors  as  far  as  both  the  cooling  and  the  lubrication  are 
concerned.  The  tendency  of  most  automobile  engines  is  to  run 
too  cool  to  be  efficient.  In  other  words,  if  they  could  be  run 
steadily  at  a  higher  temperature,  less  gasoline  would  be  used  and 
the  smaller  quantity  passing  through  the  cylinders  would  be 
employed  more  efficiently.  But  an  automobile  engine  never  runs 
steadily  for  any  length  of  time  and  it  is  very  seldom  that  more 
than  a  fraction  of  its  normal  power  output  is  used  at  all.  Except 
in  pulling  out  of  a  mud  hole  or  in  climbing  a  very  steep  hill,  it  is 
rare  for  more  than  25  per  cent  of  the  output  of  the  motor  to  be 
needed  in  driving  the  car.  Consequently  its  cooling  system  is  very 
seldom  called  upon  to  work  to  capacity. 

There  are  few  cars  built  that  could  climb  a  two-  or  three- 
mile  hill  mainly  on  second  or  even  third  speed  without  starting 
the  water  to  boiling  very  violently,  and  if  the  hill  were  five  miles 
long,  few  would  be  able  to  get  up  without  a  stop  on  the  way  to 
cool  off  the  motor.  Compared  with  the  level  road  service  that  an 
automobile  is  usually  called  upon  to  perform,  the  tractor,  par- 
ticularly when  plowing,  is  performing  the  equivalent  of  mounting 
a  steep  hill  on  second  or  third,  with  the  exception,  however,  that 
there  is  no  summit  to  the  hill  and  no  opportunity  to  cool  until  the 
motor  is  shut  down  For  the  day.  The  cooling  system  accordingly 


GASOLINE  TRACTORS  61 

calls  for  close  attention,  any  sign  of  overheating  being  noted 
immediately  and  the  engine  shut  down  at  once  to  remedy  the 
trouble.  Fan  belts  and  pumps  must  constantly  be  kept  at  a  high 
state  of  efficiency  since  slippage  at  the  fan  or  a  leaky  pump  gland 
will  reduce  the  cooling  ability  of  the  system  all  out  of  proportion 
to  the  apparent  importance  of  the  defect.  When  working  under  a 
heavy  load,  such  as  plowing  or  driving  a  good-sized  thresher,  the 
engine  cannot  be  shut  down  too  quickly  upon  the  first  indication 
of  any  trouble  writh  the  cooling  system  as  under  such  conditions 
only  a  few  minutes  are  required  to  destroy  the  film  of  lubricating 
oil  between  the  pistons  and  cylinders  and  then  the  damage  is  done. 
With  an  automobile  engine  it  is  seldom  necessary  to  add 
water  to  the  cooling  system  even  after  a  long  run  on  a  hot  sum- 
mer's day.  A  tractor  cooling  system,  on  the  other  hand,  may 
need  water  several  tunes  a  day,  and  this  is  particularly  true  of  the 
thermo-syphon  type  of  circulation  since  the  water  wrill  not  con- 
tinue to  circulate  unless  the  entire  system  is  filled  to  a  certain 
level.  The  slower  speed  at  which  the  water  circulates  in  this  type 
keeps  it  at  a  higher  average  temperature,  so  that  evaporation  is 
rapid.  The  manufacturers  of  the  Fordson,  for  instance,  recom- 
mend that  the  radiator  always  be  filled  before  starting  and  replen- 
ished every  time  the  machine  is  stopped  for  fuel  or  oil.  As  regards 
winter  use,  the  same  precautions  apply  as  in  the  case,  c.f  the  auto- 
mobile, that  is,  the  radiator  must  either  be  drained  upon  stopping 
the  motor  or  an  anti-freezing  solution  used.  Since  the  latter 
reduces  the  boiling  point  considerably,  evaporation  is  even  more 
rapid  when  running  under  full  load  on  anything  but  very  cold 
days,  so  that  it  is  better  practice  to  drain  the  system. 

IGNITION   SYSTEM. 

Importance  of  Ignition.  It  has  been  previously  stated  that 
precedence  cannot  be  given  to  any  of  the  systems  upon  which  the 
operation  of  the  motor  depends  since  the  failure  of  any -one  means 
the  stopping  of  the  motor.  It  will  be  found  in  practical  service, 
however,  that  there  are  various  degrees  of  importance  as  far  as  the 
order  in  which  the  failure  of  these  systems  may  be  responsible  for 
stopping  the  motor  is  concerned.  Considered  from  this  point  of 
view,  the  ignition  system  heads  the  list  in  that  it  is  apt  to  be  the 


62  GASOLINE   TRACTORS 

cause  of  failure  to  operate  more  frequently  than  any  of  the  others. 
There  is  no  function  of  the  motor,  a  knowledge  of  which  is  more 
important  to  the  operator  than  familiarity  with  the  principles 
involved  in  ignition,  since  without  this  knowledge  it  is  always 
much  more  difficult  to  locate  and  remedy  the  trouble.  Ignition 
breakdowns  do  not  result  in  the  serious  damage  that  attends  a 
failure  of  the  cooling  or  the  lubricating  system,  but  they  involve 
vexatious  delays  and  the  loss  of  much  valuable  time  when  the 
difficulty  cannot  be  located  quickly.  The  following  brief  review 
of  electrical  principles  is  confined  wholly  to  those  utilized  in  tractor 
operation,  and  they  should  be  thoroughly  mastered. 

Electrical  Principles 

Electric  Current.  Electricity  is  one  of  nature's  forces  possess- 
ing many  of  the  characteristics  of  light  and  heat  plus  a  number 
that  are  peculiar  to  it  alone.  Like  light  and  heat,  it  may  be  pro- 
duced by  artificial  means  in  a  number  of  different  ways.  The 
energy  it  represents  may  be  utilized  in  different  forms,  such  as 
current  or  as  magnetism.  For  ignition  purposes  the  electric  cur- 
rent is  either  produced  by  a  direct-current  generator  and  chemically 
converted  into  another  form  in  a  storage  battery  from  which  it  is 
taken  for  producing  the  spark  required,  or  it  is  generated  by  a 
magneto,  which  is  a  simple  form  of  alternating-current  generator. 
Electric  current  may  thus  be  direct  or  alternating,  and  in  either 
case  it  possesses  the  property  of  being  able  to  flow  along  or  in  a 
conductor.  In  the  former  case  it  flows  in  one  direction  around 
what  is  termed  a  circuit,  the  point  at  which  it  issues  from  the 
generator  or  battery  being  known  as  the  positive,  or  +,  pole,  and 
the  one  to  which  it  returns  being  the  negative,  or  — ,  pole.  The 
signs  +  and  -  -  are  usually  stamped  on  storage  batteries  to  indi- 
cate what  is  known  as  the  polarity  of  the  battery,  and  they  cor- 
respond to  the  north  and  the  south  poles  of  a  magnet.  ^Alternatiag 
current,  on  the  other  hand,  pulsates,  or  alternates,  first  in  one 
direction  and  then  in  the  opposite,  so  that  a  pole  which  is  positive 
at  the  beginning  of  an  alternation  becomes  negative  at  its  comple- 
tion since  the  current  then  rises  and  flows  i.i  the  opposite  direction. 
A  direct  current  is  of  uniform  strength  in  addition  to  flowing  in 
one  direction,  while  an  alternating  current  rises  from  zero  to  its 


GASOLINE   TRACTORS  63 

maximum  and  then  drops  back  to  zero  to  rise  again  in  the  opposite 
direction.  The  majority  of  tractors  are  equipped  with  magnetos, 
which  generate  an  alternating  current,  and  from  the  character  of 
such  a  current,  as  just  outlined,  the  importance  of  properly  tim- 
ing the  magneto  to  the  engine  may  be  appreciated  since  the  cur- 
rent for  producing  the  spark  is  only  present  when  an  alternation 
is  approaching  its  maximum,  or  peak.  If  the  magneto  is  improp- 
erly timed  to  the  engine,  no  spark  will  occur  at  the  plug. 

Electrical  Units.  Electricity  may  be  measured  in  units 
equivalent  to  the  pressure  and  the  rate  of  flow  of  any  other  form 
of  energy  and,  carrying  out  the  comparison,  it  also  encounters 
resistance  to  its  flow.  The  ampere  is  the  electrical  unit  of  quan- 
tity; the  volt,  that  of  force,  or  pressure;  and  the  ohm,  that  of 
resistance.  The  electrical  power  unit  is  the  wratt,  equal  to  the 
product  of  1  ampere  times  1  volt.  The  flow  of  an  electric  current 
may  be  compared  directly  to  that  of  water  under  pressure  in  a 
pipe.  The  number  of  gallons  delivered  per  minute  is  the  equiva- 
lent of  the  amperes  of  current;  the  pressure  under  which  it  is 
delivered  corresponds  to  the  voltage  of  the  current;  and  the 
resistance  to  flow  represented  by  the  friction  of  the  water  against 
the  walls  of  the  pipe  corresponds  to  the  resistance  encountered  by 
the  current  in  a  wire  or  other  conductor.  By  increasing  the  pres- 
sure on  the  water,  a  greater  volume  is  delivered  in  a  given  time. 
By  increasing  the  voltage  of  an  electric  current,  although  no 
greater  volume  of  current  is  delivered,  the  resulting  power  is  cor- 
respondingly greater  since  electrical  energy  is  represented  by  the 
product  of  the  number  of  amperes  times  the  voltage.  Moreover 
when  the  pressure  on  the  water  is  increased,  a  smaller  proportion 
of  the  total  head,  or  pressure,  is  lost  in  friction,  and  this  is  equally 
true  of  an  electric  current  since  the  higher  the  voltage,  the  smaller 
the  amount  of  electrical  energy  dissipated  in  the  wire  as  resistance. 

Conductors.  The  flow  of  an  electric  current  is  determined  by 
the  nature  of  the  material  comprising  what  is  known  as  the  cir- 
cuit. Some  materials  are  very  good  conductors,  such  as  silver, 
copper,  brass,  and  aluminum;  others  are  poor  conductors,  such  as 
iron,  nickel,  and  alloys  containing  a  high  percentage  of  these  metals; 
while  still  other  materials,  such  as  glass,  porcelain,  mica,  rubber, 
wood,  and  stone,  will  not  conduct  the  current  at  all  when  dry. 


64 


GASOLINE   TRACTORS 


The  latter  are  insulators  and  are  used  to  prevent  the  passage  of 
the  current  where  this  is  not  desired;  for  example,  part  of  the 
spark  plug  is  made  of  porcelain.  The  ability  of  a  material  to 
conduct  electric  current  is  determined  by  its  size  as  well  as  by  its 
nature.  Given  two  pieces  of  wire  of  the  same  size,  one  of  copper 
and  the  other  of  iron,  the  copper  wire  will  conduct  the  current 
approximately  thirty  times  easier  than  the  iron.  By  increasing 
the  iron  wire  to  thirty  times  the  size  of  the  copper  wire,  both  will 
then  conduct  the  same  current  and  voltage  with  the  same  amount 
of  resistance.  Iron  and  nickel  are  accordingly  high  resistance 
conductors,  preventing  the  free  flow  of  the  current  and  converting 
a  large  part  of  the  energy  represented  by  the  latter  into  heat, 


Fig.  32.     Simple  Series  Circuit  Representing  Ignition  System  -of  Single-Cylinder   Motor. 
The  Parallel  Lines  are  Ground  Return  through  the  Motor 

which  explains  why  a  piece  of  iron  wire  will  not  serve  as  well  for  a 
magneto  or  battery  connection  as  the  copper  wire  supplied  by  the 
manufacturer.  In  addition  to  the  insulators  already  mentioned,  no 
fabric  such  as  silk,  cotton,  and  wool  will  pass  current  when  dry, 
while  dry  air  is  the  best  insulator  known. 

Circuits.  It  has  already  been  mentioned  that  a  current  flows 
from  the  positive  to  the  negative  pole  of  the  source  of  energy,  but 
in  order  for  it  to  do  so  there  must  be  a  complete  circuit  of  con- 
ducting material  between  the  two,  a  current  of  low  voltage  being 
considered  in  this  connection.  The  presence  of  any  insulators  in 
the  path  of  the  current  accordingly  prevents  its  flow,  and  since  air 
is  one  of  the  best  insulators,  any  break  in  the  current  such  as  a 
parted  wire  or  a  loose  connection  admits  air  and  interrupts  the 


GASOLINE   TRACTORS 


65 


flow  of  current.  If  the  material  comprising  the  conducting  path, 
or  circuit,  be  of  high  resistance,  the  flow  of  current  will  be  either 
greatly  reduced  or  prevented  altogether  in  the  case  of  the  low- 
tension  currents  employed  in  ignition.  If  a  conductor  of  high 
resistance,  such  as  a  very  small  piece  of  wire,  occurs  in  the  circuit 
of  a  storage  battery,  it  is  likely  to  melt  owing  to  the  heat  generated 
by  its  resistance. 

Ignition  Circuits.  Ignition  circuits  are  of  but  one  kind,  that 
is,  series  circuits  in  which  all  the  pieces  of  apparatus,  such  as  the 
magneto,  the  coil,  and  the  plugs,  form  successive  steps  through 
which  all  the  current  must  pass  in  order  to  complete  the  circuit. 
Simple  forms  of  series  circuits  are  illustrated  in  Figs.  32  and  33, 
which  show  a  dry  battery,  coil,  and  plug  used  as  a  starting  system 


\\\ 


Fig.  33.     Series  Circuit  Using  Low-Tension  Magneto  for 
Single-Cylinder  Ignition  System 

for  a  tractor  and  a  low-tension  magneto,  coil,  and  plug  constitut- 
ing a  complete  ignition  system.  When  a  battery  is  employed  for 
lighting  to  carry  on  night  work  as  well  as  for  ignition,  two  inde- 
pendent series  circuits  may  be  fed  from  the  same  source,  the 
amount  of  current  taken  by  each  being  determined  by  the  resist- 
ance that  it  presents  to  the  flow  of  the  current.  A  multiple,  or 
parallel,  circuit  is  one  in  which  lamps,  motors,  or  other  apparatus 
may  be  inserted  at  any  point,  each  unit  being  connected  to  oppo- 
site sides  of  the  circuit,  so  that  any  unit  may  draw  current  inde- 
pendently of  the  others.  Connections  may  be  taken  at  any  point 
on  opposite  sides  of  such  a  circuit  to  form  a  branch  circuit  and 
the  apparatus  in  the  branch  circuit  connected  in  series,  resulting 
in  what  is  termed  a  multiple-series  circuit. 


66  GASOLINE  TRACTORS 

Voltage  and  Amperage.  The  pressure  under  which  the  cur- 
rent flows  is  termed  its  voltage,  and  this  may  be  determined 
either  by  the  source  of  supply  or  by  the  presence  of  a  transformer 
in  the  circuit.  In  the  case  of  a  battery  the  voltage  depends  upon 
the  number  of  cells  connected  in  series  with  one  another,  while  the 
amperage,  or  volume  of  current,  is  measured  by  that  of  any  one 
cell  in  the  series.  For  example,  dry  cells  deliver  a  current  at  1J 
volts  and  ordinarily  average  15  amperes  for  short  periods.  A 
battery  of  four  dry  cells  in  series  would  thus  produce  a  current  of 
15  amperes  at  6  volts.  If  the  cells  were  connected  in  multiple,  that 
is,  all  the  positives  together  and  all  the  negatives  together,  the 
current  would  be  increased  but  the  voltage  would  be  that  of  a 
single  cell,  so  that  there  would  be  a  current  of  60  amperes  at  li 
volts. 

Storage  Battery.  In  the  case  of  a  storage  battery  which 
delivers  current  at  2  volts  per  cell,  the  voltage  required  for  igni- 
tion, that  is,  6  volts,  is  obtained  by  connecting  three  cells  in 
series,  while  the  volume  of  current  depends  upon  the  capacity  of 
the  individual  cells  in  the  series,  and  this  in  turn  is  measured  by 
their  size.  For  ignition  service  cells  of  a  battery  are  always  con- 
nected in  series,  so  that  the  positive  of  one  cell  must  be  connected 
to  the  negative  of  the  next,  and  so  on  throughout  the  series,  one 
terminal  of  the  battery  being  positive  and  the  other  negative. 
Any  cross  connection  in  the  series,  such  as  the  connection  of  the 
positive  of  one  cell  to  the  positive  of  the  next,  would  cause  one 
part  of  the  battery  to  act  against  the  remainder,  with  the  result 
that  no  current  would  be  delivered  to  the  outside  circuit. 

Magneto.  The  voltage  of  the  magneto  or  any  other  mechani- 
cal current-generating  device  is  determined  by  the  speed  of  its 
armature.  The  magneto  illustrates  the  fact  that  electricity  and 
magnetism  are  different  forms  of  the  same  force  in  that  one  may 
be  readily  converted  into  the  other.  By  moving  a  magnet  close  to 
a  coil  of  wire,  a  current  of  electricity  is  induced  in  the  wire,  while 
if  a  coil  of  wire  is  placed  about  a  bar  of  iron  or  steel  and  an 
eleetric  current  is  then  passed  through  the  wire,  the  bar  becomes 
magnetic.  Steel  retains  a  considerable  percentage  of  the  magne- 
tism after  the  current  ceases  and  is  termed  a  permanent  inaunet. 
The  fields  of  a  magneto  are  formed  of  permanent  magnets  and 


GASOLINE   TRACTORS  67 

supply  the  magnetism  by  means  of  which  a  current  is  generated 
when  the  wire  on  the  armature  is  moved  past  their  pole  pieces, 
that  is,  their  north  and  south  poles.  Therefore  a  magneto  will 
generate  a  current  at  any  speed,  but  the  amount  of  current  and 
the  voltage  under  which  it  flows  depend  upon  the  speed  with 
which  the  armature  is  revolved.  The  strength  of  a  magnet  is 
represented  by  imaginary  lines  passing  from  one  pole  to  the  other, 
and  these  are  termed  lines  of  force.  The  voltage  of  the  magneto 
current  is  determined  by  the  number  of  times  per  minute  that  the 
wires  of  the  armature  cut  through  the  lines  of  force  between  the 
magnet  poles. 

Low=  and  High=Tension  Currents.  The  foregoing  brief  expla- 
nation has  been  confined  to  what  are  known  as  low-voltage  cur- 
rents, the  storage  battery  delivering  current  at  6  volts  for  ignition, 
while  the  magneto  when  running  at  full  speed  generates  current  at 
approximately  100  to  125  volts.  Any  current  under  500  volts  is 
usually  referred  to  as  a  low- volt  age  current.  In  connection  with 
the  explanation  of  insulators  it  has  been  mentioned  that  the 
interposition  of  any  insulating  material  in  the  circuit,  and  partic- 
ularly a  break  or  loose  connection  which  creates  an  air  gap, 
interrupts  the  flow  of  current.  This  is  true  of  all  low-voltage 
currents;  all  parts  of  the  circuit  must  be  not  merely  connected  but 
in  firm  and  positive  contact,  and  the  contact  surfaces  must  be 
clean  and  bright  since  dirt  is  likewise  an  insulator.  This  is  a 
principle  frequently  overlooked  in  the  care  of  tractor  and  farm 
engines,  which  usually  work  in  very  dusty  places;  it  is  absolutely 
necessary  to  keep  all  connections  •  clean  and  tight  to  insure  the 
satisfactory  working  of  the  ignition  system. 

Since  even  a  loose  connection  will  interrupt  the  flow  of  current 
in  a  low-voltage  circuit,  it  is  not  suitable  for  the  production  of  a 
spark  unless  the  terminals  representing  the  positive  and  negative 
sides  of  the  circuit  are  actually  brought  into  contact  and  then 
separated.  What  is  known  as  the  low-tension  system  of  ignition 
is  emoloyed  on  thousands  of  stationary  farm  engines  and  also  on 
many  tractors  having  low-speed  engines.  Most  stationary  engines 
are  run  at  low  speeds,  ranging  from  200  or  less  to  450  r.p.m., 
while  few  tractor  engines  run  below  600  r.p.m.  at  normal  speed 
and  most  of  them  operate  at  much  higher  speeds. 


68 


GASOLINE   TRACTORS 


Types  of    Ignition   Systems, 

Low=Tension  Ignition.     While  dry  cells  may  be  employed  for 
ignition   with   a   stationary   engine   equipped   with   a  hit-and-miss 

governor  that  cuts  off  the  cur- 
rent except  on  the  power  strokes, 
they  do  not  give  satisfactory 
service  and  therefore  a  magneto 
is  generally  used.  The  magneto 
chosen  is  the  simplest  type  and 
consists  of  nothing  more  than 
the  field  pieces,  or  permanent 
magnets,  and  a  simple  armature 
having  a  single  winding.  It 
may  either  be  rotated  or  given 
a  quick  partial  revolution  by 
a  rod  and  spring,  but  in  any 
case  it  must  be  timed  to  the 
engine,  so  that  the  current  in 
its  armature  is  at  the  maximum 
value  when  the  spark  is  to  occur 
in  the  cylinder.  While  such  a 
magneto  produces  ample  cur- 
rent  at  a  fair  voltage  it  is  not 
sufficient  to  produce  a  spark  of 
the  desired  size  for  low-tension 
ignition,  and  therefore  a  spark 
coil  is  placed  in  the  circuit. 

Spark  Coil.  The  spark  coil 
consists  of  a  single  winding  of 
many  layers  of  heavy  insulated 
wire  on  a  thick  short  core  built 
up  of  fine  iron  wire  that  has 
been  annealed  until  it  is  very 
soft,  as  in  this  condition  it  is 
capable  of  being  magnetized  and 

very  quickly.  Such  ti  coil  acts  on  the  principle  of  self- 
induction  and  produces  a  much  hotter  and  larger  spark  than  the 
magneto  could  unaided.  Its  working  will  be  clear  from  Fig.  34, 


GASOLINE   TRACTORS  69 

which  shows  a  typical  low-tension  ignition  system.  Up  to  the 
time  it  is  necessary  for  the  spark  to  occur  in  the  cylinder,  the 
ignitor  has  its  points  in  contact,  so  that  the  circuit  is  closed  and 
current  flows  through  the  ignitor  and  the  winding  of  the  spark 
coil.  Consequently  the  core  of  the  coil  is  magnetized  and  stores 
up  the  equivalent  of  the  current  which  magnetized  it.  When  the 
circuit  is  broken  by  the  sudden  snapping  of  the  ignitor,  this  mag- 
netism is  instantly  reconverted  into  electric  current  and  adds  its 
force  to  that  of  the  current  in  the  winding,  and  a  much  hotter 
spark  results  at  the  contacts.  In  fact,  this  is  really  a  flash  instead 
of  a  spark  and  is  usually  termed  an  arc;  and  it  is  so  hot  that  it 
burns  the  contact  points  away  rapidly,  which  is  one  of  the  dis- 
advantages of  the  low-tension  system. 

High=Tension  Ignition.  In  high-tension  ignition  the  ignitor  of 
the  low-tension  system  is  replaced  by  a  spark  plug  with  fixed 
electrodes,  or  terminals,  separated  by  an  air  gap.  But  in  order 
that  the  current  may  bridge  this  gap,  it  is  necessary  to  raise  it 
to  a  high  voltage.  This  ranges  all  the  way  from  10,000  to  30,000 
volts,  the  higher  voltage  being  necessary  when  the  initial  com- 
pression of  the  engine  is  high  since  a  greater  electrical  tension  is 
required  to  create  a  spark  across  a  gap  in  compressed  air  than 
out  in  the  open. 

Induction  Coil.  In  the  brief  reference  given  to  elementary  elec- 
trical principles  it  has  been  mentioned  that  when  a  coil  of  wire  is 
passed  before  a  magnet,  a  current  of  electricity  is  induced  in  the 
wire.  This  also  occurs  either  wdien  one  coil  of  wire  in  circuit 
through  which  a  current  is  flowing  is  moved  close  to  another  in 
which  there  is  no  current  or,  the  two  coils  being  stationary, 
when  the  current  is  suddenly  broken  in  the  first.  This  is  the 
basic  principle  of  the  transformer,  or  induction  coil.  As%  in  the 
case  of  the  spark  coil,  the  effect  produced  is  greatly  increased  by 
using  a  heavy  core  of  soft-iron  wire.  The  character  of  the  current 
induced  in  the  second  coil  depends  upon  the  relation  that  the 
windings  of  the  latter  bear  to  those  of  the  coil  in  which  the 
current,  termed  the  primary  current,  is  flowing.  If  both  coils 
have  the  same  number  of  turns  in  their  windings,  the  induced,  or 
secondary,  current  will  be  approximately  the  same  in  amperes  and 
volts  as  the  primary  current.  By  increasing  the  number  of  turns 


70  GASOLINE   TRACTORS 

in  the  secondary  winding  of  the  coil,  the  voltage  of  the  induced 
current  will  be  increased  correspondingly.  An  induction  coil 
accordingly  consists  of  a  comparatively  few  turns  of  heavy  wire 
for  the  primary  winding,  which  is  closer  to,  though  insulated 
from,  the  soft-iron  core.  The  secondary  coll  consists  of  a  great 
number  of  turns  of  very  fine  wire  and  surrounds  the  primary 
winding,  but  it  must  also  be  well  insulated  from  the  latter,  as 
otherwise  the  high  tension-current  would  tend  to  jump  from  the 
windings  of  one  to  the  other.  A  coil  in  which  this  has  occurred 
is  said  to  be  punctured  and,  as  it  is  short-circuited,  is  useless  for 
ignition  until  repaired. 

Mechanisms  to  Make  and  Break  Circuit.  Where  batteries 
are  employed  for  ignition  or  the  magneto  generates  a  current 
which,  though  alternating  in  its  nature,  is  of  such  high  frequency 
as  to  be  practically  continuous,  as  on  the  Fordson  tractor,  the 
induction  coil  must  be  equipped  with  a  vibrator  to  make  and 
break  the  circuit  since  current  is  only  induced  in  the  secondary 
winding  when  the  circuit  is  broken  or  the  current  rises  and  falls 
from  zero  to  maximum  and  the  reverse,  as  in  an  alternating 
current  of  lower  frequency.  In  what  is  known  as  the  modern 
battery  system,  employing  a  storage  battery  kept  charged  by  a 
small  direct-current  generator,  a  primary  contact  breaker  in  con- 
nection with  the  distributor  takes  the  place  of  the  coil  vibrator 
and  but  one  coil  is  used. 

Essential  Parts  of  System.  A  high-tension  system  accordingly 
consists  of  a  source  of  current,  most  often  a  magneto,  a  coil,  a 
spark  plug  for  each  cylinder,  and  a  distributor.  The  distributor 
always  forms  a  part  of  the  magneto  and  is  driven  by  the  magneto 
shaft,  and  in  what  is  known  as  the  true  high-tension  type  of 
magneto  the  coil  is  also  incorporated  with  it;  that  is,  the  magneto 
generates  the  primary  low-tension  current  and  also  transforms  it 
or  steps  it  up  to  the  required  high  voltage,  the  armature  usually 
carrying  both  the  primary  and  the  secondary  windings.  Conse- 
quently with  a  high-tension  magneto  the  complete  ignition  system 
consists  of  the  magneto  itself,  the  spark  plugs,  and  the  necessary  con- 
necting cables,  so  that  the  entire  system  is  practically  self-contained. 

Condenser.  A  part  of  the  high-tension  system  with  which  the 
operator  is  not  likeh  to  become  acquainted  unless  something  goes 


GASOLINE  TRACTORS  71 

wrong  with  it  is  the  condenser.  In  the  form  employed  for  igni- 
tion the  condenser  consists  of  alternate  leaves  of  tinfoil  and  par- 
affined paper,  the  latter  serving  to  insulate  the  sheets  of  tinfoil 
from  one  another.  The  tinfoil  sheets  are  divided  into  two  groups, 
which  are  connected  to  opposite  sides  of  the  contact  breaker  of 
the  magneto,  so  that  the  condenser  is  in  multiple  with  the  breaker. 
(Magneto  parts  and  construction  are  explained  in  detail  in  con- 
nection with  the  description  of  some  of  the  standard  makes 
employed  for  tractor  ignition.)  When  parts  in  contact  carrying 
current  are  suddenly  separated,  a  flash,  or  arc,  occurs  owing  to 
the  tendency  of  the  current  to  continue  its  flow  across  the  break, 
as  happens  in  a  low-tension  ignitor.  This  not  only  represents*  a 
loss  of  energy  but  tends  to  burn  away  the  parts.  To  prevent 
this,  a  condenser  is  shunted  about  the  contact,  that  is,  connected 
in  multiple  with  it.  The  current,  instead  of  continuing  across  the 
gap  in  the  form  of  an  arc  as  the  contacts  open,  flows  into  the 
condenser,  which  has  the  capacity  to  store  a  charge  of  electricity. 
Immediately  upon  the  contact  being  made  again  so  as  to  reclose 
the  circuit,  this  stored  charge  flows  back  from  the  condenser  into 
the  circuit. 

Safety  Spark  Gap.  In  the  explanation  of  circuits  mention 
has  been  made  of  the  fact  that  a  current  divides  or  flows  through 
different  branches  of  a  circuit  in  proportion  to  the  resistance  in 
those  branches.  In  other  words,  it  will  always  seek  the  path  of 
least  resistance.  Consequently,  if  the  air  gap  of  a  spark  plug  be 
made  so  large  that  it  represents  a  resistance  greater  than  the 
insulation  of  the  windings  of  the  coil,  whether  this  coil  be  sepa- 
rate or  on  the  armature  of  the  magneto,  the  current  will  break 
down  the  insulation  and  short  circuit  the  winding.  The  current 
burns  away  the  electrodes  of  the  spark  plugs  and  the  gap  must  be 
adjusted  from  time  to  time  to  correct  this;  at  the  most  the  gap 
should  not  exceed  the  thickness  of  a  visiting  card,  or  -^  inch. 
As  the  gap  widens,  the  spark  becomes  thinner  and  loses  its  heat 
value  so  that  the  ignition  is  less  and  less  satisfactory.  When  at 
last  the  gap  becomes  so  wide  as  to  present  a  greater  resistance 
than  the  coil  insulation,  the  spark  will  jump  across  the  safety 
spark  gap  provided  to  protect  the  coils.  This  gap  is  designed 
with  an  opening  having  a  resistance  that  is  considerably  less  than 


72 


GASOLINE  TRACTORS 


that  of  the  coil  insulation  so  as  to  allow  an  ample  margin  of 
safety  for  the  coils.  It  is  usually  located  under  the  arch  of  the 
magnets  of  a  high-tension  magneto  and  is  mounted  on  the  dis- 
tributor of  a  modern  battery  ignition  system.  The  occurrence  of 
a  spark  across  this  gap  is  an  indication  that  one  or  more  of  the 
spark  plugs  have  been  burned  open  too  far,  though  this  will 
usually  be  evident  from  the  poor  ignition  resulting. 

Low=Tension  Magneto.  Magneto  ignition  has  proved  the 
most  dependable  as  well  as  the  most  enduring  for  tractor  work 
since  the  excessive  vibration  and  jolting  make  the  use  of  the 
storage  battery  practically  out  of  the  question.  Dry  cells  are  of 
little  value  in  any  case  for  ignition,  except  where  starting  is  con- 
cerned, and  the  necessity  for  them  has  been  eliminated  by  the 
development  of  the  impulse  starter  on  the  magneto,  as  described 


Fig.  35.     Inside  and  Outside  Views  of  Low-Tension  Ignition  Plug 
Used  on  Oil-Pull  Tractor 

later.     There  are  several  types   of    magnetos    in   general  use  on 
the  tractor  and  a  brief  reference  is  made  to  each  of  them. 

On  tractors  employing  low-speed  horizontal  engines,  low- 
tension  ignition  is  .standard  equipment.  It  has  the  advantage  of 
being  extremely  simple  and  all  its  parts  can  be  made  amply  strong 
enough  to  withstand  the  strenuous  treatment  of  tractor  service  in 
the  field.  Its  chief  disadvantage  is  the  more  or  less  frequent 
necessity  for  attention  to  the  ignitors,  though  the  hot  flash  pro- 
duced by  the  latter  is  better  adapted  to  ignite  low-grade  fuels 
than  the  high-tension  spark  produced  by  a  plug.  The  magneto 
employed  with  the  low-tension  system  has  but  one  winding  and 
no  contact  breaker  nor  distributor.  It  is  connected  in  a  simple 
series  circuit  with  a  spark  coil  and  the  ignitors.  The  Bosch  low- 
tension  magneto  is  the  type  employed  on  the  Ruinely  tractor. 


GASOLINE  TRACTORS 


73 


In  Fig.  35  are  given  two  views  of  an  ignitor,  the  view  at 
the  left  showing  the  tripping  mechanism  outside  the  cylinder, 
while  that  at  the  right  shows  the  details  of  the  fixed  and  movable 

IGN/TJON  SPOOL  SfOP-J  /flDJVSTING  SCREW -5 
/GMT/ON  SPOOL;? 

HL 


ELECTRODE  F/NGER- 


-/GM/T/ON PLUG -4 

Fig.  36.     Tripping  Mechanism  of  Low-Tension  Igniter,  Electrodes  in  Contact  before  Sparking 

electrodes  between  which  the  spark  occurs  when  they  are  suddenly 
snapped  apart.  In  Figs.  36  and  37  are  shown  the  details  of  the 
tripping  device,  the  former  illustrating  the  mechanism  with  the 
electrodes  in  contact  just  before  sparking. 

Timing  of  Low-Tension  System.  Since  the  magneto  is  directly 
connected  in  a  simple  series  circuit  with  each  ignitor,  it  is  evident 
that  both  the  latter  and  the  magneto  itself  must  be  timed  to 
produce  the  spark  at  the  proper  moment  for  the  explosion.  The 


/GN/TIOM  SPOOL  STOP~ 
/GN/TtON  SPOOL  -2 

f\ 


ADJUSTING  SCREW-5 

'GN/T/ON  TR/PPEft-6 


-/GMT/ON  PLUG -4 

Fig.  37.     Low-Tension  Ignitor  Tripping  Mechanism,  Showing  Adjustment  Spacing 

ignitor  is  tripped  by  a  push  rod  and  cam  on.  the  camshaft  in 
exactly  the  same  manner  as  the  valves  are  operated,  while  the 
magneto  itself  is  timed  to  the  motor  in  much  the  same  manner 


74 


GASOLINK   TRACTORS 


as  is  necessary  in  the  case  of  a  high-tension  magneto.  In  the 
section  on  elementary  electricity  it  has  been  explained  how  an 
alternating  current  rises  from  zero  to  maximum  in  one  direction 

and  then  subsides  and  rises 
again  in  the  opposite  direc- 
tion. This  is  termed  a  sine- 
wave  current  and  is  illus- 
trated  by  Fig.  38.  The  only 
part  of  this  current  that  is 
of  value  for  ignition  is  repre- 


Fig. 08.     Sine  Wave  Alternating  Cur- 
rent as  Generated  by  Magneto 


sented  by  the  few  degrees  in 
the  revolution  of  the  arma- 
ture that  are  indicated  by 
the  peaks  of  the  alternations.  In  a  simple  magneto  with  an  H 
armature,  Fig.  39,  this  peak  occurs  at  the  point  shown  in  the 
illustration,  that  is,  the  point  when  the  core  of  the  armature  is 
entering  the  tunnel  formed  by  the  pole  pieces  attached  to  the  field 
magnets  at  their  lower  ends. 

In  Fig.  39  the  armature  is  turning  to  the  left  and  has  just 
left  the  right-hand  pole  piece  by  YG  inch.     From  this  point  until 

the  center  of  the  core  of  the 
armature  is  on  a  line  with  the 
upper  part  of  the  pole  piece,  the 
value  of  the  current  is  close  to 
the  peak  and  is  rising.  The 
further  revolution  of  the  armature 
causes  it  to  fall,  and  when  the 
core  reaches  the  lower  part  of  the 
tunnel,  it  reverses  and  starts 
upward  in  the  opposite  direction. 
The  armature  of  the  magneto 
must  accordingly  be  set  so  that  it 
is  in  the  position  shown  in  the 

Fkg.30  Motion    if    Armature  illustl'at i()ll     when    tllC     igllitor     is 

about  to  trip.  This  is  not  the  maximum,  as  the  armature  cuts 
the  greatest  number  of  magnetic  lines  of  force  a  few  degrees 
further  around  and  thus  produces  the  current- of  the  greatest 
value  at  that  point.  This  setting  allows  for  the  necessary  advance 


ARMATURE-L 


GASOLINE   TRACTORS  75 

of  the  sparking  time,  which  causes  the  latter  to  coincide  with  the 
point  of  maximum  value  just  mentioned. 

Causes  of  Trouble  Few.  There  being  only  a  current  of  very 
low  voltage  in  any  part  of  the  system  and  only  a  single  short 
wire  being  necessary  to  conduct  this  low-tension  current  to  the 
ignitors,  electrical  troubles  are  rare  with  the  low-tension  system 
and  are  confined  chiefly  to  failure  of  the  ignitors,  or  make-and- 
break  plugs,  to  spark  owing  to  an  accumulation  of  carbon,  or 
soot,  on  the  electrodes.  Apart  from  this,  any  shortcomings  of  the 
system  are  apt  to  be  purely  mechanical  rather  than  electrical. 
The  tripping  mechanism  and  springs  must  necessarily  be  light, 
but  at  the  speeds  at  which  they  operate  wear  is  more  or  less 
rapid,  so  that  considerable  attention  is  required  to  maintain  them 
in  efficient  operating  condition.  This  is  the  chief  reason  why  the 
low-tension  ignition  is  not  applicable  to  the  high-speed  type  of  motor. 

As  before  stated,  most  of  the  electrical  difficulties  experienced 
with  the  low-tension  system  involve  the  ignitors,  or  make-and- 
break  plugs.  Unless  the  fuel  is  being  burned  very  efficiently  by 
the  engine,  they  short-circuit  very  quickly  through  a  deposit  of 
carbon,  although  this  also  occurs  at  regular  intervals  even  where 
it  is  not  possible-  to  improve  upon  the  running  of  the  engine. 
Another  cause  of  trouble  is  the  sticking  together  of  the  electrodes 
by  what  is  practically  a  form  of  electric  welding.  Carbon  deposits 
must  be  scraped  off  carefully,  electrode  contact  surfaces  filed  or 
scraped  bright,  and  the  remainder  of  the  plug  cleaned  with  kero- 
sene. After  a  considerable  time  in  service  the  mica  insulation  of 
these  plugs  may  become  so  impregnated  with  carbon  dust  or  a 
mixture  of  oil  and  carbon  dust  that  it  is  impossible  to  prevent  it 
short-circuiting,  in  which  case  it  is  necessary  to  replace  the  mica 
insulation.  The  plugs  are  the  source  of  the  trouble  in  about  85 
per  cent  of  the  cases,  but  when  they  are  in  good  condition,  the 
magneto  should  be  tested,  first,  to  note  whether  it  is  generating 
or  not  and,  second,  to  see  whether  it  is  properly  timed  to  the 
engine.  To  provide  sufficient  current  at  a  good  voltage,  the 
plug  must  snap,  or  break,  just  at  the  moment  when  the  current 
in  the  armature  of  the  magneto  is  close  to  the  peak,  Fig.  39. 
The  maximum  current  and  voltage  are  generated  when  the  arma- 
ture has  turned  a  few  degrees  further. 


76  GASOLINE   TRACTORS 

Testing  Low- Tension  Magneto.  To  test  the  armature  to  find 
out  whether  it  is  generating  or  not,  attach  a  short  piece  of  copper 
wire  to  its  terminal,  place  the  bare  end  of  this  wire  against  the 
field  magnet,  and  rotate  the  armature.  Pull  the  wire  away  from 
time  to  time,  and  a  good  spark  will  follow  if  the  magneto  is  in 
good  order.  If  this  proves  to  be  the  case  and  the  spark  still 
fails  to  occur  at  the  plug,  the  position  of  the  armature  should  be 
noted  at  the  moment  that  the  plug  breaks,  and  if  this  does  not 
correspond  with  the  position  shown  in  Fig.  39,  the  magneto 
should  be  retimed.  The  plug  itself  may  be  tested  by  taking  it 
out  and  laying  it  on  the  cylinder.  With  the  magneto  running, 
the  electrodes  may  be  snapped  apart.  Should  they  fail  to  spark, 
all  other  parts  of  the  system  being  in  good  working  order,  it  is 
usually  due  to  the  insulation  of  the  plug.  A  spare  plug  should 
be  inserted  and  the  insulation  of  the  old  one  replaced  as  soon  as 
the  opportunity  arises.  By  carrying  spares,  much  valuable  time 
in  the  field  may  be  saved. 

High=Tension  Magnetos.  Two  Types.  Two  types  of  high- 
tension  magnetos  are  employed  for  tractor  ignition:  one  in  which 
both  windings  are  placed  directly  on  the  core  of  the  H-type 
armature,  so  that  the  windings,  core,  and  condenser  rotate 
together;  and  the  other,  the  so-called  inductor  type  in  which  the 
winding  is  stationary  while  the  rotor  in  two  parts  revolves  on 
either  side  of  it.  The  first  type  illustrates  the  elementary  elec- 
trical principle  that  rotating  a  coil  of  wire  through  the  lines  of 
force  of  a  magnetic  field  will  induce  a  current  in  the  wire.  The 
current  thus  induced  in  the  primary  winding  of  the  coil  on  the 
armature  is  tnmsfonned  to  one  of  high  voltage  by  the  secondary 
winding  which  is  also  on  the  armature.  The  gear  shown  at  the 
right-hand  end  of  the  armature  is  for  the  purpose  of  driving  the 
distributor  disc,  the  function  of  which  is  explained  later. 

The  rotor  and  winding  of  an  inductor  type  of  magneto,  the 
K-W,  are  shown  in  Fig.  10,  while  a  phantom  view  of  the  complete 
machine  is  given  in  Fig.  41.  It  will  l>e  noted  in  Fig.  40  that  the 
rotor  consists  of  two  blocks  of  iron  placed  at  right  angles  to  one 
another  with  the  winding  between  them.  In  Fig.  41  the  con- 
denser is  at  the  left  of  the  winding,  while  the  contact  box  and 
the  distributor  of  the  magneto  are  at  the  right.  The  operation  of 


GASOLINE   TRACTORS 


77 


the  inductor  type  of  magneto  is  based  on  the  principle  that 
rotating  a  magnet  so  that  its  lines  of  force  cut  the  winding  of  a 
coil  will  induce  a  current  in  the  latter.  The  magnet  in  this  case 
is  the  rotor,  the  members  of  which  form  part  of  the  magnetic 
circuit  of  the  machine.  They  are  most  strongly  magnetic  when  in 
the  position  at  which  the  current  of  any  magneto  is  at  the  maxi- 
mum, as  previously  explained  in  connection  with  the  low-tension 
magneto.  The  rotor  takes  its  magnetism  from  the  permanent 
magnets  of  the  field  in  the  same  way  that  an  ordinary  horseshoe 


Fig.  40.     Rotor  of  K-W  Inductor  Motor 
Courtesy  of  K-W  I;/ nil  ion  Company,  Cleveland,  Ohio 

magnet  will  render  an  iron  nail  magnetic  as  long  as  they  are  in 
contact. 

High- Tension  Circuit.  The  wiring  of  a  true  high-tension 
magneto,  that  is,  one  that  has  both  the  primary  and  the  secondary 
windings  embodied  in  the  magneto  itself,  is  almost  as  simple  as  that 
of  the  low-tension  type  already  described;  in  the  high-tension 
system  one  wire  is  necessary  for  each  plug  and  in  the  low-tension 
system  a  single  cable  connected  to  a  busbar  in  contact  with  all 
the  ignitors  is  needed.  But  in  the  high-tension  system  these  wires 
carry  current  at  very  high  voltage  and  the  slightest  defect  in  the 
insulation  or  the  presence  of  dampness  is  apt  to  permit  this  high- 
tension  current  to  leak  away,  usually  without  giving  any  sign  of 
its  escape. 

The  primary  circuit  of  a  high-tension  system  consists  of  the 
primary  winding  on  the  armature,  whether  stationary  or  rotating, 


78 


GASOLINE   TRACTORS 


the  condenser,  and  the  contact  breaker.  The  secondary  circuit 
consists  of  the  secondary  winding  (whether  located  on  the  arma- 
ture of  the  magneto  itself  in  the  form  of  a  coil  placed  under  the 
arch  of  the  magnets  in  the  magneto  or  placed  independently  of 
the  magneto),  the  distributor,  the  cables  leading  to  each  of  the 
spark  plugs,  and  the  safety  spark  gap.  It  will  be  noted  that 
each  case  represents  but  one  side  of  a  circuit.  The  other  side- 
is  grounded,  that  is,  the  current  returns  through  the  metal  of  the 
magneto  in  the  primary  circuit  and  through  that  of  the  motor 


Fig.  41.     Phantom  View  of  Complete  K-W  Inductor  Magneto 

Ciiurtr::i/  nf  A"- 1'/  lynition  Company,  Cleveland,  Ohio 

and  the  magneto  in  the  secondary.  Thus  a  spark  plug  with  a 
cable  attached  completes  the  circuit  when  it  is  screwed  into  the 
cylinder. 

Contact  Hmikrr.  Regardless  of  detailed  differences  in  their 
construction  or  design,  all  high-tension  magnetos  operate  on  the 
same  principles,  and  in  every  case  the  contact  breaker  is  the  part 
of  the  magneto  on  which  its  continued  operation  depends.  In 
Fig.  42  is  shown  a  complete  high-tension  ignition  system  con- 
Ming  of  a  K  \Y  magneto  and  its  connections  for  a  four-cylinder 
motor.  The  contact  breaker  details  are  plainly  shown  just  below 
the  distributor  of  the  magnet^,:  C  is  a  cam  carried  on  the  end  of 
the  magneto  armature  shaft;  R  is  a  roller  carried  at  the  center  of  a 
hinged  arm  which  is  pivoted  at  its  right-hand  end  and  is  designed 


GASOLINE   TRACTORS 


79 


to  minimize  wear  on  the  cam.  At  its  left-hand  end  this  same 
hinged  arm  carries  a  platinum  contact  point  designed  to  make 
contact  with  a  similar  point  that  is  held  stationary,  but  is  adjusta- 
ble for  wear.  The  hinged  arm  and  the  stationary  contact  point 
are  attached  to  the  contact  breaker  box  A,  which  may  be  turned 
through  a  partial  revolution  in  either  direction  to  advance  or 
retard  the  time  of  sparking. 

The  circuit  through  the  primary  winding  on  the  armature  is 
completed  when  the  contact  points  P  are  together,  and  it  will  be 


-ENGINE  CYL/NDERS 

SECONDARY  W/ftES  TO 
5/^/f/f  PLUGS 


MAGNETO 

Fig.  42.     Ignition  Circuit  of  Four-Cylinder  Motor 
Courtesy  of  K-W  Ignition  Company,  Cleveland,  Ohio 

noted  that  they  are  in  contact  with  each  other  as  long  as  the 
cam  C  is  horizontal,  so  that  current  is  flowing  in  this  circuit. 
When  the  cam  C  turns  so  that  it  becomes  vertical,  it  corresponds 
to  the  position  of  maximum  current  in  the  armature  winding  and 
the  circuit  is  suddenly  opened  at  that  moment.  This  breaking  of 
the  current  provides  the  impulse  necessary  to  induce  the  maxi- 
mum current  and  voltage  in  the  secondary  winding.  At  the  same 
moment  that  the  contact  breaker  opens,  provided  the  motor  is 
designed  to  turn  to  the  right,  or  clockwise,  the  distributor  contact 
B  is  passing  close  to  S,  which  is  the  terminal  representing  the 
spark  plug  of  cylinder  1.  If  it  is  a  left-handed  motor,  the^dis- 


80 


GASOLINE   TRACTORS 


tributor  contact  B  will  be  at  the  sparking  point  for  cylinder  4 
at  S'.  There  is  accordingly  a  path  open  for  the  high-tension 
current  to  the  spark  plug.  As  the  distributor  is  driven  directly 
from  the  armature  of  the  magneto  by  gearing,  Fig.  43,  the  dis- 
tributor contact  is  at  a  point  corresponding  to  the  cylinder  that  is 
to  be  fired  each  time  the  contact  breaker  opens. 

Firing  Order.  While  these  points  on  the  distributor  are  num- 
bered consecutively  from  1  to  4,  the  cylinders  of  a  four-cylinder 
motor  cannot  be  fired  in  that  order  since  the  cranks  of  a  four- 
cylinder  four-cycle  motor  are  spaced  at  180°.  In  other  words, 
there  are  two  in  one  plane  and  the  other  two  are  in  the  plane 


Fig.  43.     Distributor  End  of  K-W  Magneto 
Courtesy  cf  K-W  Ignition  Company,  Cleveland,  Ohio 

opposite,  or  half  a  revolution  away.  Consequently,  cylinders  in 
the  same  plane  cannot  follow  one  another  in  firing.  This  is  made 
plain  in  the  circuit  diagram,  Fig.  42.  From  this  illustration  it  is 
evident  that  cylinders  1  and  4  have  their  cranks  in  the  same 
plane,  so  that  the  cylinder  to  fire  after  cylinder  1  must  be  either 
2  or  3.  It  will  also  be  noted  that  contact  3  of  the  distributor 
corresponds  to  cylinder  4  of  the  motor,  so  that  the  firing  order 
of  this  motor  is  1,  2,  4,  3.  The  firing  order  most  commonly 
adopted  for  four-cylinder  motors  is  1,  3,  4,  2  since  this  produces 
a  somewhat  better  impulse  balance  by  distributing  the  successive 
explosions  among  cylinders  at  equidistant  points  on  the  crankshaft. 
In  checking  up  the  ignition  or  making  any  repairs  it  is  important 


GASOLINE  TRACTORS  81 

to  know  what  the  firing  order  of  the  motor  is,  and  this  will  usually 
be  found  stamped  on  it  in  some  conspicuous  place. 

Care  of  Magneto.  Since  modern  high-tension  magnetos  have 
their  shafts  mounted  on  ball-bearings,  they  require  very  little  oil 
and  that  only  at  infrequent  intervals.  A  few  drops  once  a  week 
in  the  case  of  some  and  once  in  two  weeks  with  others  is  all 
that  is  necessary  so  far  as  lubrication  is  concerned. 

The  contact  breaker  is  the  most  important  part  of  the  mag- 
neto and  is  the  one  that  should  be  looked  to  first  whenever  the 
magneto  fails  to  deliver  a  spark  at  the  plugs,  all  other  essentials 
of  the  system  being  in  good  condition.  Long  continued  operation 
at  full  load  is  apt  to  burn  the  contact  points  away  to  such  an 
extent  that  they  do  not  come  together  when  the  cam  is  in  the 
horizontal  position.  Or  they  become  so  pitted  and  covered  with 
oxidizing  material,  which  insulates  them,  that  the  current  cannot 
pass  even  though  they  make  contact.  The  contact  points  should 
be  kept  true  and  bright  with  a  very  fine  thin  file  or  with  a  strip 
of  fine  sandpaper,  taking  care  to  remove  all  traces  of  dust  from 
the  contact  box  by  cleaning  it  out  with  gasoline  or  kerosene. 
Since  the  points  are  made  of  very  expensive  material,  when  they 
are  trued  up  no  more  metal  should  be  removed  than  is  necessary 
to  bring  the  surfaces  squarely  together.  Much  better  service  will 
be  obtained  from  the  magneto  if  this  operation  is  carried  out  at 
frequent  intervals,  say  once  a  month  when  the  tractor  is  being 
used  steadily,  instead  of  waiting  until  the  points  get  in  such  a 
condition  that  the  magneto  will  not  operate  at  all.  If  the  contact 
points  burn  away  very  rapidly,  it  is  an  indication  that  the  con- 
denser has  broken  down  and  should  be  replaced.  This  is  usually 
a  job  that  must  be  referred  to  the  magneto  manufacturer.  Apart 
from  the  attention  required  by  the  contact  breaker,  the  only  care 
that  it  is  necessary  to  give  the  magneto  is  to  keep  it  clean  and  well- 
oiled  and  see  that  its  connections  are  always  tight. 

Spark  Plugs.  Regardless  of  how  well  every  other  part  of 
the  ignition  system  is  working,  a  spark  will  not  occur  in  the  cylin- 
der unless  the  spark  plugs  are  in  good  condition.  The  spark 
plug  is  the  business  end  of  the  entire  system  since  its  failure  will 
render  useless  the  perfect  functioning  of  every  other  part.  As 
will  be  noted  in  the  sectional  view,  Fig.  44,  a  spark  plug  consists 


82 


GASOLINE   TRACTORS 


of  two  electrodes  with  a  gap  between  them  across  which  the 
current  must  jump  in  order  to  ignite  the  fuel  in  the  cylinder. 
One  of  these  electrodes  is  the  outer  shell  of  the  spark  plug  itself 
and  completes  the  circuit  through  the  ground  return  when  it  is 
screwed  into  the  cylinder  head.  The  other,  or  central  electrode, 
is  connected  directly  with  one  of  the  points  on  the  high-tension 
distributor  of  the  magneto,  so  that  the  path  of  the  current  is 
down  through  this  central  electrode,  across  the  gap  to  form  the 
spark  and  back  through  the  body  of  the  motor  to  the  magneto, 
which  is  also  grounded  by  being  bolted  to  the  motor. 

Importance  of  Insulation.  No  spark  plug  can  be  any  better 
than  the  insulation  which  separates  the  two  electrodes  since  the 
entire  operation  of  the  plug  depends  upon  its  pre- 
venting the  escape  of  the  current  before  reaching 
the  gap.  Like  any  other  force  under  pressure,  elec- 
tricity will  always  seek  the  line  of  least  resistance, 
and  as  compressed  air  has  a  higher  electrical  resist- 
ance than  any  solid  insulator,  the  slightest  leak  in 
the  insulation  will  open  a  path  for  the  current  and 
no  spark  will  occur  at  the  gap. 

Heat,  vibration,  hot  oil,  and  soot  are  all  enemies 
of  the  insulation,  and  under  their  combined  attack- 
it  is  bound  to  break  down  sooner  or  later.  Soot, 
or  carbon,  which  is  an  excellent  conductor  of  elec- 
tricity, is  the  commonest  cause  of  spark-plug  failure, 
but  it  does  not  necessarily  put  the  plug  out  of 
commission  for  good.  It  is  particularly  difficult  to 
prevent  the  accumulation  of  carbon  on  the  ends  of  the  plugs  in 
an  engine  burning  kerosene,  but  a  good  cleaning  with  a  fine  wire 
brush  and  plenty  of  gasoline  is  usually  all  that  is  necessary  to 
restore  them  to  service. 

Common  Plug  Troubles.  Apart  from  the  difficulty  of  short- 
circuiting  due  to  carbon  collecting  on  the  ends  of  the  plugs,  the 
commonest  causes  of  trouble  are  due  to  a  hidden  breakdown  of 
the  insulation  and  to  the  burning  away  of  the  electrode  points, 
so  that  the  resistance  of  the  gap  becomes  too  great  for  the  current 
to  bridge.  Porcelain  is  one  of  the  best  insulators  known  for  the 
purpose,  but  it  is  difficult  to  make  a  porcelain  that  will  witli- 


Fig.  44.     Sectional 

View  of  a  Spark 

Plug 


GASOLINE   TRACTORS  83 

stand  the  intense  heat  and  the  vibration  indefinitely,  particularly 
as  the  material  is  already  under  stress  due  to  the  screwing  down 
of  the  gasket  nut  of  the  plug  in  order  to  make  it  gas  tight. 
When  it  becomes  intensely  hot,  the  vibration  and  pounding  are 
apt  to  open  fine  invisible  cracks  in  the  body  of  the  porcelain. 
The  carbon  is  forced  into  these  and  forms  a  conducting  path  for 
the  current.  As  this  carbon  cannot  be  cleaned  out,  the  plug  is 
useless  until  a  new  porcelain  has  been  inserted. 

In  the  same  manner,  the  hot  oil  carrying  a  considerable  per- 
centage of  carbon  particles  is  forced  into  the  mica  insulation  of 
a  plug  until  it  becomes  so  impregnated  with  this  conducting 
material  that  it  will  no  longer  spark.  Only  the  replacement  of 
the  electrode  and  its  insulator  will  cure  the  trouble.  Failure  to 
spark  due  to  the  electrode  points  having  been  burned  too  far 
apart  sometimes  makes  itself  apparent  by  the  current  visibly 
passing  over  the  outside  of  the  plug.  That  is,  instead  of  jump- 
ing the  gap  inside  the  cylinder,  the  current  finds  a  path  of  less 
resistance  across  the  surface  of  the  insulator.  This  will  sometimes 
occur  when  a  plug  gets  extremely  hot,  even  though  the  points 
are  properly  spaced,  and  since  water  is  a  good  conductor,  it  will 
always  take  place  if  the  slightest  amount  of  moisture  is  allowed 
to  fall  on  the  porcelain  of  the  plugs.  Dirty  oil  will  also  provide 
a  conducting  path.  When  the  electrode  points  have  burned  too 
far  apart  and  no  indication  is  visible  at  the  plug  itself,  the  spark 
will  be  noticed  jumping  the  safety  spark  gap  on  the  magneto. 

Under  the  continued  heavy  service  of  a  tractor  engine  that 
is  being  used  for  plowing  ten  hours  a  day  and  six  days  a  week, 
it  will  be  nothing  unusual  to  have  to  adjust  the  spark  plug 
points  two  or  three  times  a  week,  particularly  where  cheap  plugs 
are  used,  since  the  electrodes  are  of  common  iron  and  burn  away 
very  quickly.  It  is  poor  economy  to  buy  cheap  spark  plugs,  though 
it  is  not  so  great  a  sin  as  to  buy  cheap  lubricating  oil.  The  latter 
besides  damaging  the  motor  in  other  wrays  will  cause  added 
trouble  with  spark  plugs  of  any  kind  owing  to  the  excessive 
amount  of  carbon  that  accumulates  in  the  cylinders.  Leakage  of 
compression  through  the  plugs  must  be  prevented  by  turning 
down  the  nut  at  the  base  of  the  porcelain  to  seat  it  on  the 
gasket,  but  this  must  be  done  carefully  or  the  porcelain  will  break. 


84  GASOLINE   TRACTORS 

Wiring.  Moisture  and  oil  are  also  enemies  of  the  insulation 
of  the  high-tension  cables  that  connect  the  distributor  terminals 
of  the  magneto  with  the  plugs.  These  cables  must  be  kept  clean 
and  dry  and  their  terminals  at  both  ends  must  be  kept  tight 
with  the  cables  in  a  position  where  they  do  not  come  into  con- 
tact with  one  another  or  with  the  body  of  the  engine  as  far  as 
possible  since  despite  the  thickness  of  the  rubber  and  the  cotton 
insulation  the  high-voltage  current  will  find  a  path  through  it  at 
the  slightest  opportunity.  When  the  cables  have  become  soaked 
with  oil  and  dirt,  it  is  better  to  discard  them  and  replace  them 
with  an  entire  new  set  as  the  value  of  the  insulation  has  been 
destroyed  to  a  large  extent. 

In  order  to  make  the  cables  flexible,  they  are  made  up  of  a 
large  number  of  fine  copper  wires  stranded  together.  When  the 
cables  become  frayed  at  the  ends  next  to  the  plug  terminals, 
particularly,  it  is  nothing  unusual  for  one  or  more  of  these  very 
fine  strands  of  copper  to  project  against  the  body  of  the  plug  or 
some  other  metal  and  thus  cause  a  short-circuit  that  is  not 
noticeable.  Both  ends  of  the  cables  should  be  well  taped  at  the 
terminals  to  prevent  this.  Contact  with  any  moving  parts  must 
be  avoided  as  even  a  slight  amount  of  wear  on  the  insulation 
will  lower  its  resistance  to  a  point  where  the  current  will  find  a 
path  through  it.  This  is  particularly  true  of  cuts  that  penetrate 
both  the  cotton  and  the  rubber,  but  which  may  be  so  small  as 
to  be  imperceptible.  Despite  their  size  the  current  will  leak 
through  them  if  the  cables  come  in  contact  with  any  metal 
parts  since  almost  any  path  of  this  kind  will  present  less  resist- 
ance than  does  the  gap  of  the  spark  plug,  especially  when  the 
latter  has  been  burned  open 'too  far. 

Magneto  Impulse  Starter.  Owing  to  the  fact  that  it  is  not  found 
practical  in  the  majority  of  instances  to  carry  a  storage  battery  on 
a  tractor,  while  the  average  tractor  motor  cannot  be  cranked  fast 
enough  by  hand  to  start  it  with  the  ordinary  magneto,  an  attach- 
ment has  been  designed  for  the  latter  .by  means  of  which  it  may 
be  caused  to  generate  sufficient  current  for  a  hot  spark  regardless 
of  the  speed  of  the  engine.  This  is  known  as  an  impulse  starter. 
It  consists  of  a  spring  mechanism,  which,  when  the  engine  is 
cranked,  is  automatically  released,  causing  the  magneto  armature 


GASOLINE  TRACTORS  85 

to  turn  through  a  partial  revolution  much  more  rapidly  .than  the 
crankshaft. 

Bosch.  The  details  of  the  Bosch  impulse  starter  are  shown  in 
Fig.  45,  while  Fig.  46  illustrates  the  magneto  complete  as  equipped 
with  the  starter.  Referring  to  the  detail  view  Fig.  45,  it  will  be 
noted  that  a  dish-shaped  flange  is  attached  to  the  armature  shaft 
and  that  this  flange  carries  two  cams  on  its  periphery.  In  the 
view  at  the  right  is  shown  the  crossbar  member  which  forms  an 
integral  part  of  the  starter  driving  shaft.  The  squared  ends  of 
this  bar  fit  the  openings  of  the  flange  mentioned.  This  bar  floats 
on  the  helical  springs  shown,  which  are  held  in  a  circular  recess 
and  are  secured  to  the  starter  shaft,  which  is  also  the  main  driv- 


Fig.  45.     Details  of  Bosch  Impulse  Starter 

Courtesy  of  American  Bosch  Magneto  Corporation, 

Springfield,  Massachusetts 

ing  shaft,  as  is  made  clear  in  the  assembled  view  of  the  magneto. 
The  operation  of  this  starter  is  controlled  by  a  latch  forming  part 
of  '  the  external  engagement  lever,  which  is  .shown  projecting 
upward.  When  it  is  not  desired  to  operate  the  impulse  starter, 
this  latch  is  held  away  from  the  cams  by  a  trigger.  Releasing  the 
trigger  drops  the  latch,  and  the  starter,  or  coupling  shaft,  is 
revolved,  causing  the  spring  to  be  compressed.  Since  the  crossbar 
is  held  stationary,  the  armature  does  not  revolve.  By  moving  the 
small  lever  to  the  release  position,  the  springs  are  freed  and  they 
give  a  rapid  partial  turn  to  the  magneto  armature.  When  the 
engine  speed  exceeds  150  r.p.m.,  the  speed  at  which  the  cams 
strike  the  lever  is  sufficient  to  cause  it  to  fly  up  out  of  the  posi- 
tion where  it  is  held  by  the  trigger,  so  that  the  magneto  operates 


80  GASOLINE  TRACTORS 

in  the  usual  manner.  For  starting  large  engines,  it  is  customary 
to  prime  the  cylinders  with  gasoline;  the  impulse  starter  lever  is 
then  moved  over  to  the  engaged  position  and  let  go.  The  engine 
is  cranked  to  bring  the  piston  in  a  cylinder  that  is  about  to  fire  a 
few  degrees  beyond  the  upper  dead  center  on  the  firing  stroke-, 
and  then  the  starter  lever  is  pushed  to  the  release  position,  caus- 
ing a  spark  to  occur  in  the  cylinder  under  compression.  To  facili- 
tate starting  in  this  manner,  a  check  mark  may  be  made  on  the 
My  wheel  to  indicate  the  starting  position. 

/•'iwmann.  In  Fig.  47  is  illustrated  the  mechanism  of  the 
Kisemann  magneto  impulse  starter,  in  which  a  spiral  spring  is 
employed  as  the  driving  element.  For  greater  clearness,  this 


Fig.  4(>.     Bosch  Magneto  Equipped  with  Impulse  Starter 

Courtesy  nf  Awn'rati   Bosch  Magneto  Corporation,  Xpringfirlil, 

Massachusetts 

spring  is  indicated  by  dotted  lines.  The  spring  N  is  attached  to 
the  members  II  and  (',  the  former  being  the  housing  attached  to 
the  magneto  shaft  and  the  latter  the  driving  member;  J>  is  a  fixed 
bar  which  is  mounted  on  the  base  of  the  magneto;  and  7  is  a 
floating  member,  or  trigger.  When  the  motor  is  cranked  slowly, 
the  trigger  T  drops  by  gravity,  engaging  the  bar  II  and  temporarily 
preventing  the  rotation  of  the  housing  //.  Since  C  is  driven  by 
the  engine,  cranking  causes  it  to  compress  the  spring,  or  wind 
it  up,  until  the  cam  on  ('  strikes  the  wedge  IF.  This  forces  the 
trigger  upward  until  it  slips  off  the  lower  bar,  thus  releasing  the 
housing  //  and  causing  the  spring  to  give  the  armature  a  sharp 
partial  turn.  The  right-hand  illustration  shows  the  relation  of  the 


GASOLINE  TRACTORS 


87 


members  after  the  spring  has  been  released  and  the  magneto 
starter  is  in  its  normal  running  position.  Stops  are  provided  on 
the  housing  and  the  outer  part  of  the  driver  C  to  prevent  the 
armature  from  being  turned  past  the  position  it  must  maintain  to 
be  properly  timed  to  the  engine.  To  hold  the  starter  out  of 
operation  while  the  engine  is  running,  T  is  heavily  counterbalanced 
and  as  a  result  the  action  of  centrifugal  force  on  it  draws  the  part 
T  further  in  until  the  detent  on  it,  shown  just  above  the  trigger 


ig.  47.      Impulse  Starter  on  Eiscmann  Magneto 

< '<»ir!(.--i/  of  Eixrnxiini  .l/V/'/Mr/n  C'nmjtnn )i,  Rr»nkh/n,  Nnv  York 

itself,  enters  the  notch  N  in  the  driving  member  C,  where  it  is 
held  as  long  as  the  magneto  runs  at  its  normal  speed.  As  this 
notch  provides  a  positive  drive  for  the  magneto  independently  of 
the  spring,  the  starter  acts  merely  as  a  coupling  when  running. 

TYPES   OF    MOTORS 

Wide  Range  of  Types.  When  gasoline-driven  tractors  were 
first  placed  on  the  market  with  a  view  to  providing  a  machine 
that  could  be  more  widely  used  than  the  steam  tractor,  they  con- 
sisted of  little  more  than  a  single-cylinder  stationary  gasoline 
engine  on  wheels.  While  tractor  design  has  advanced  considerably 
since  that  time,  it  is  still  a  long  way  from  having  reached  any 
standard  as  far  as  the  power  plant  is  concerned.  Meanwhile,  the 
automobile  engine  has  undergone  tremendous  improvement,  while 
its  manufacture  is  now  carried  out  on  a  scale  that  was  not  dreamed 
of  fifteen  years  ago.  As  a  result,  the  tractor  engine  has  been 
developed  under  the  influence  of  two  widely  separated  standards, 


88  GASOLINE  TRACTORS 

first,  that  of  the  stationary  engine  builder  and  second,  that  of  the 
automobile  engine  manufacturer.    There  is,  consequently,  a  wide 


Fig.  48.     Two-Cylinder  Horizontal  Motor  Used  on  20-40  Oil-Pull  Tractor 
Courtesy  of  Advance-Rumely  Thrcshfr  Company,  Inc.,  Laporte,  Indiana 


Fig.  49.     Interior  of  Crank  Case,  Oil-Pull  Motor 
Courtesy  of  Adtance-Rumchj  Thresher  Company,  Inc.,  Laporte,  Indiana 

range  of  engine  types  used  for  tractor  propulsion.  At  one  end  of 
this  range  there  is  the  descendant  of  the  original  stationary 
engine,  made  more  compact  and  with  additional  cylinders  to  provide 


GASOLINE  TRACTORS 


89 


the  needed  extra  power  without  excessive  weight,  while  at  the  other 
extreme  there  is  the  light,  high-speed,  multi-cylinder  motor,  which 
to  all  intents  and  purposes  is  practically  an  automobile  engine. 
Horizontal  Engine.  Oil-Pull.  To  a  large  extent  the  horizon- 
tal engine  is  an  outgrowth  of  stationary  engine  practice.  A  repre- 


Fig.  50.     Section  of  Eagle  Two-Cylinder  Horizontal  Motor 
Courtesy  of  Eagle  Manufacturing  Company,  Appleton,  Wisconsin 

sentative  example  is  illustrated  in  Fig.  48,  which  shows  the  20-40 
Oil-Pull  engine.  The  cylinders  are  cast  with  separable  heads  and 
the  valves,  located  in  the  latter,  are  operated  by  rocker  arms. 
The  carburetor,  or  fuel  mixer,  the  magneto,  the  force-feed  oiler, 
and  the  circulating  pump  are  all  placed  on  top  of  the  motor  for 


90  CASOLIXK   TRACTORS 

greater  accessibility.  Since  splash  lubrication  cannot  be  used 
owing  to  the  position  of  the  cylinders,  force-feed  oilers  with  leads 
directly  to  each  of  the  bearings  are  commonly  used  on  this  type 
of  engine.  In  Fig.  49,  is  shown  a  head-on  view  of  the  same  motor 
with  the  crankcase  removed,  showing  the  crankshaft  and  bearings, 
the  camshaft  and  timing  gears.  The  magneto,  the  circulating 
pump,  and  the  force-feed  oiler  are  also  driven  by  the  gears.  In 
this  engine  the  cylinders  are  slightly  offset  to  reduce  the  pressure 
on  the  cylinder  walls  during  the  firing  stroke. 

Eagle.     A  clearer  idea  of  the  internal  details  of  this  type  of 
engine  is  obtainable  from  the  sectional  view,  Fig.  50,  showing  an 


Fig.  51.     Avery  Two-Cylinder  Horizontal  Opposed  Motor 
Courtesy  of  Arery  Company,  Prnrin,  Illinois 

Kagle  two-cylinder  motor.  The  upper  cylinder  has  been  sectioned 
through  the  center  line  of  the  piston,  showing  the  piston  pin  and 
the  inside  of  the  valve  cages,  while  the  lower  one  illustrates  the 
complete  piston  with  its  rings  and  the  removable  valve  cages  in 
the  cylinder  head.  Whether  it  be  horizontal  or  vertical,  one  of 
the  advantages  of  the  valve-in-head  type  of  motor  is  the  ease  with 
which  the  valves  may  be  kept  in  condition,  grinding-in  being  an 
operation  that  must  be  carried  out  at  frequent  intervals  on  a 
tractor  engine. 

Horizontal-Opposed  Awry.  The  horizontal  opposed  type  was 
largely  used  on  automobiles  for  several  years  during  the  early 
period  of  their  development  in  this  country.  It  provides  better 
impulse  and  mechanical  balance  than  the  two-cylinder  type  in  which 


Fig.  52.     Engine  of  Holt  Caterpillar  Tractor 
Courtesy  of  Holt  Manufacturing  Comp'inu,  Inc.,  Peoria, 


Fig.  53.     Parts  of  Tracklayer  Tractor  Engine 
Courtesy  of  C.  L.  Best  Gas  Tractor  Company,  San  Leandro,  California 


92 


GASOLINE   TRACTORS 


the  cylinders  are  placed  side  by  side  and  is  accordingly  freer  from 
vibration.  In  Fig.  51  is  illustrated  the  A  very  two-cylinder  motor 
of  this  type,  which  is  also  built  with  four  cylinders  in  the  larger 
sizes.  A  novel  feature  of  the  Avery  motor  that  overcomes  the 
disadvantage  to  which  this  type  was  subject  on  the  automobile  is 


Fig.  54.     Automobile  Type  Engine  of  Parrett  Tractor 
Courtesy  of  Parrett  Tractor  Company,  Chicago  Height?,  Illinois 

the  use  of  removable  cylinder  liners.  Owing  to  the  weight  of  the 
piston  resting  on  the  lower  half  of  the  cylinder  wall  the  latter 
wore  out  of  round  more  rapidly  than  would  the  cylinders  of  a  ver- 
tical engine  in  the  same  service.  This  destroyed  the  compression 
and  involved  the  reboring  of  the  cylinders  and  the  fitting  of  over- 
size pistons.  The  A  very  cylinder  liners  are  cast  of  harder  metal 


GASOLINE   TRACTORS 


93 


than  the  cylinders  themselves  and  may  be  given  a  part  turn  from 
time  to  time  so  as  to  distribute  the  wear  over  the  entire  wall, 
while  the  liner  itself  may  be  replaced  readily. 

Vertical  Motors.  Holt  and  Tracklayer.  All  the  horizontal 
motors  described  are  specially  designed  for  tractor  service  by  the 
manufacturers  of  the  tractors  themselves  and  produced  in  their 
own  shops.  With  comparatively  few  exceptions,  most  of  the  ver- 
tical types  of  tractor  motors  are  the  products  of  the  various  large 


Fig.  55.     Section  of  Moline  Four-Cylinder  Motor 
Courtesy  of  Moline  Plow  Company,  Moline,  Illinois 

automobile  motor  factories  and  are  designed  along  lines  that 
closely  follow  practice  in  the  automobile  field.  One  of  these 
exceptions  is  the  Holt  motor  shown  in  Fig.  52,  while  another  of 
very  similar  design  is  the  power  plant  of  the  Tracklayer  tractor. 
Some  of  the  construction  details  of  this  motor  are  shown  in 
Fig.  53,  which  illustrates  a  cylinder  casting,  cylinder  head  with 
valves,  piston,  piston  pin,  and  the  cylinder  head  and  manifold 
gaskets.  Both  of  these  motors  are  specially  designed  and  built 


94 


GASOLINE  TRACTORS 


for  tractor  service  and  are  of  the  slow-speed  type  best  adapted  for 
carrying  a  large  percentage  of  their  maximum  load  continuously. 
Parrett.    The   Parrett   motor   shown   in   Fig.    54,    while   also 
designed  for  this  service,  follows  automobile  practice  more  closely. 
It  is  shown  with  the  cylinder  head  casting  and  the  crankcase  oil 
pan    removed    to    illustrate    the    accessibility    thus    obtained.     Its 
smaller  size  and  greater  compactness  is  accounted  for  by  the  fact 
,  .      that   it   is   a   high-speed   type,   de- 

signed to  produce  its  normal  rated 
output  at  1000  r.p.m. 

Moliw'.  Another  motor  of  this 
class  is  the  Moline,  which  is  shown 
in  longitudinal  section  in  Fig.  55 
and  in  cross-section  in  Fig.  ">(>. 
These  illustrations  are  taken  from 
the  Moline  instruction  book  and 
the  identification  figures  serve  to 
make  clear  the  functions  of  the 
various  parts  of  a  motor.  From 
1  to  J  in  Fig.  55  they  refer  to 
the  lubricating  system,  as  follows: 
1,  oil  level  in  crankcase;  2,  suction 
pipe  to  oil  pump;  3,  oil  pump;  /h 
oil  conduit  drilled  through  the 
crankshaft;  and  5,  oil  lead  to  crank- 
pin  bearings.  Numbers  6  and  7 
are  the  driving  pinion  and  gear  o! 
the  timing  gear;  8,  a  bevel  gear  for 
the  belt  pulley  of  the  tractor;  9,  a 
valve  tappet;  10,  the  valve  mech- 
anism chamber;  and  11,  the  oil 
cap  filler  and  breather.  The  latter  admits  air  to  the  crankcase  and 
is  a  necessary  feature  of  all  motors  but  is  usually  located  directly 
on  the  crankcase  itself.  It  is  one  of  the  points  that  must  be  care- 
fully guarded  against  the  entrance  of  dust  and  grit  to  the  interior 
of  the  motor. 

In  Fig.  5(>   /   is  the  oil  screen;  J,  the  suction  pipe  to  the  oil 
pump;  .1,  the  oil  hole  to  the  rrankpin  bearing;  ./,  the  crankshaft; 


Fin.  ~>G.   Cross-Section  of  Moline  Motor 
Courtesy  of  Moline  Plow  Company, 

Mnlinr.  Illinois 


GASOLINE  TRACTORS 


95 


5,  the  crankpin;  6,  the  combustion  chamber  of  one  cylinder;  7,  a 
valve;  8,  the  valve  spring;  9,  the  rocker  arm  of  the  valve  linkage; 
and  11,  the  rocker  arm  stud;  10  is  the  intake  passage.  The  details 
of  the  crankshaft  and  piston  assembly  are  shown  in  Fig.  57,  in 
which  1  is  the  oil  outlet  hole  from  the  drilled  crankshaft  at  the 
forward  crankshaft  bearing;  2,  the  oil  intake  hole  at  the  rear 


Fig.  57.     Crankshaft  and  Piston  Assembly  of  Moline  Motor 

crankshaft  bearing;  3,  a  series  of  threads  designed  to  work  the  oil 
backward  into  the  crankcase  and  prevent  its  entrance  into  the 
clutch  housing;  5,  the  helical  half-time  gear  for  driving  the  cam- 
shaft and  auxiliaries;  and  6,  the  bevel  pinion  for  driving  the  belt 
pulley.  The  bolts  for  fastening  the  flywheel  to  the  crankshaft 
flange  are  identified  by  4- 


GASOLINE  TRACTORS 

PART  II 


CONTROL   SYSTEM 
ENGINE   GOVERNORS 

Need  of  Governors.  Plowing.  In  order  that  a  tractor  may 
be  operated  most  economically,  it  must  be  capable  of  one-man 
control  since,  in  plowing,  conditions  are  continually  encountered 
where  the  driver's  attention  must  be  centered  on  the  management 
of  the  plows  and  the  steering  of  the  machine  to  the  exclusion  of 
everything  else.  Moreover  the  demands  upon  the  engine  are  con- 
tinually varying  even  when  the  soil  conditions  are  apparently  uni- 
form for  long  stretches.  Stones,  roots,  and  extra  heavy  patches 
of  sod  all  impose  considerable  extra  load  on  the  engine  that  can 
be  met  satisfactorily  only  by  an  automatically  controlled  throttle 
if  a  uniform  plowing  speed  is  to  be  maintained. 

Belt  Work.  A  far  greater  load  variation  is  encountered  in 
belt  work  than  in  plowing,  as  in  the  former  the  engine  may  be 
running  practically  idle  at  one  moment  and  be  almost  choked 
down  by  overloading  the  next,  whereas  in  the  latter  there  is 
always  a  load  on  the  engine  and  therefore  the  danger  of  racing  is 
absent.  Irregular  speed  under  changing  load,  racing  of  the  idle 
engine,  and  tardy  opening  of  the  throttle  to  meet  the  increased 
load,  all  of  which  are  unavoidable  with  hand  control,  represent 
conditions  of  operation  which  not  only  reduce  production  at  the 
machine  being  driven  but  are  very  bad  for  the  engine  itself  as 
they  result  in  overheating,  prevent  proper  lubrication,  and,  not 
infrequently,  result  in  burned-out  bearings.  In  any  case  the  pro- 
vision of  a  governor  on  the  engine  releases  a  hand  for  other  and 
more  productive  labor.  The  majority  of  tractors  go  into  service 
in  the  hands  of  an  unskilled  operator,  and  unless  there  is  a  governor 
on  the  engine,  his  course  of  instruction  is  likely  to  be  marked  by 
the  occurrence  of  more  or  less  damage  that  automatic  control 
would  prevent. 


98 


GASOLINE   TRACTORS 


Centrifugal  Governors.  Despite  almost  innumerable  attempts 
to  displace  it,  the  centrifugal  principle  first  taken  advantage  of 
more  than  a  century  ago  to  control  the  speed  of  a  steam  engine  is 
still  in  almost  universal  use  for  this  purpose.  Most  tractor 
engines  are  equipped  with  what  is  commonly  termed  a  fly-ball 
governor,  though  the  details  of  the  mechanism  and  the  character 
of  the  throttle  valve  it  is  employed  to  control  differ  more  or  less. 
In  its  simplest  form  such  a  governor  consists  of  two  weights  on 
the  end  of  oppositely  placed  arms  which  are  pivoted  on  a  spindle 
connected  to  the  throttle  valve,  either  directly  or  through  suitable 
linkage,  so  that  any  movement  of  the  weights  is  communicated 
directly  to  the  throttle.  On  a  stationary  engine  the  governor  may 


Fig.  58.     Simplex  Engine  Governor 
< '<nirti'.--i/  <if  Duplex  Engine  Governor  Company,  Brooklyn,  New  York 

be  placed  upright  and  is  not  subjected  to  vibration  or  jolting,  so 
that  gravity  alone  may  be  depended  upon  to  keep  the  weights  in 
their  normal  position,  but  on  the  tractor  springs  are  usually 
employed,  and  the  governor  may  then  be  placed  in  any  position. 
When  running  below  a  certain  speed,  either  gravity  or  the  pull  of 
the  spring  is  sufficiently  strong  to  keep  the  weights  together  against 
the  shaft  or  close  to  it.  But  as  the  speed  increases,  centrifugal 
force  acts  on  the  weights  and  tends  to  make  them  assume  a  posi- 
tion at  right  angles  to  the  shaft.  The  faster  the  engine  runs,  the 
closer  the  weights  approach  to  this  position,  but  as  their  move- 
ment brings  about  a  proportionate  closing  of  the  throttle,  the 
engine  is  not  given  an  opportunity  to  increase  its  speed.  A  well- 
balanced  u'ovcrnor  of  this  type  will  operate  so  sensitively  that 


GASOLINE   TRACTORS  99 

there  will  be  practically  no  perceptible  change  in  speed  between 
idling  and  full  load.  So  far  as  the  tractor  is  concerned,  centrif- 
ugal governors  are  of  two  general  types,  those  that  are  an  inte- 
gral part  of  the  design  of  the  engine  and  are  built  right  into  it 
and  those  that  are  in  the  nature  of  auxiliary  devices  designed  to 
be  attached  to  the  inlet  manifold  between  the  carburetor  and  the 
intake  valves. 

Auxiliary  Types.  The  Simplex  governor,  shown  in  Fig.  58, 
and  the  Pierce,  illustrated  in  Fig.  59,  are  examples  of  governors 
designed  to  be  adapted  to  any  make  of  motor,  the  only  modifica- 
tion necessary  depending  upon  the  details  of  the  drive,  since  the 
governor  must  be  driven  directly  from  the  motor  itself.  In  the 


Adjusting  Screw  Diaphragm  Bali  Bearing 


Bell 
Cran* 


Shaf 


Spring 


Fig.  59.     Section  of  Pierce  Engine  Governor 
Courtesy  of  Pierce  Governor  Company,  Anderson*  Indiana 

Simplex  the  governor  weights,  which  are  housed  in  the  casing  just 
under  and  to  the  left  of  the  oil  plug  shown,  operate  a  grid  valve 
the  openings  of  which  appear  in  the  intake  manifold  flange  at  the 
left.  The  driving  attachment,  designed  in  this  instance  for  a 
flexible  shaft  drive,  appears  at  the  right.  Fig.  GO  shows  the 
attachment  of  a  Simplex  governor  to  a  Continental  motor,  the 
drive  in  this  case  consisting  of  a  solid  shaft  and  bevel  gears 
operating  from  the  camshaft.  The  governor  is  set  for  the  maxi- 
mum speed  to  which  the  motor  on  which  it  is  mounted  is  best 
adapted  and  is  then  sealed,  as  shown  at  the  left  end.  As  the 
governor  mechanism  runs  in  a  bath  of  oil,  it  requires  no  attention 
vxt-ept  to  replenish  the  oil  from  time  to  time, 


Fig.  60.     Installation  of  Simplex  Governor  on  Continental  Motor  of  Bullock  Tractor 
Courtesy  of  Bullock  Tractor  Company,  Chicago,  Illinois 


Fiji.  (>1 .     Installation  of  Pierce  Governor  on  Buda  Motor 
Courtesy  of  Pierce  Governor  Company,  Anderson,  Indiana 


101 


GASOLINE  TRACTORS 


The  Pierce  governor,  which  is.1  sh</\vn,  iij  tK-jr 
operates  a  conventional  butterfly  type  of  throttle  valve  such  as  is 
used  in  the  majority  of  carburetors.  This  valve  is  shown  at  the 
left,  while  the  weights  and  the  driving  attachment  are  at  the  right. 
Between  the  two  is  the  spring  against  which  the  centrifugal  force 
of  the  revolving  weights  must  act  to  close  the  throttle.  Just  above 


Fig.  62.     Built-in  Governor  of  Creeping-Grip  Tractor 
Courtesy  of  Bullock  Tractor  Company,  Chicago,  Illinois 

the  left-hand  end  of  this  spring  will  be  noted  a  screw  adjustment 
by  means  of  which  the  speed  for  which  the  governor  is  set  may  be 
altered.  Increasing  the  tension  of  the  spring  by  screwing  this  in 
permits  an  increase  in  the  speed  of  the  motor  since  the  weights 
must  then  revolve  at  a  higher  speed  in  order  to  overcome  the  pull 
of  the  spring.  This  is  the  principle  upon  which  the  adjustment  of 


102 


TRACTORS 


all   ccntT:('i:u';!   gn\  rrno'-s  is  based.     One  method  of  attaching  the 
Pierre  governor  is  illustrated  in  Fig.  61,  which  shows  it  mounted 

on  a  Buda  motor  and  driven 
through  bevel  gearing  from  the 
camshaft. 

Built-in  Types.  The  part 
sectional  end  view  of  the  engine 
of  the  Creeping  Grip  tractor, 
Fig.  62,  illustrates  an  excellent 
example  of  a  built-in  governor. 
This  is  driven  from  a  transverse 
shaft  which  takes  its  power 
through  helical  cut  gearing  from 
the  timing  gear  of  the  motor,  the 
same  shaft  also  serving  as  the  magneto  drive.  In  expanding, 
the  revolving  weights  draw  in  the  sliding  shaft  shown,  which  is 
linked  to  a  bell-crank  lever  at  its  outer  end.  The  lever  is  attached 
to  the  throttle,  which  will  be  noted  just  to  the  right  of  the  carbn- 


Mir.  IK5.     Governor  and  Magnetic  Unit  of 

Creeping-Grip  Tractor  Motor 

Conrtrxy  of  Bullock   Tractor  Compn-n;/, 

Chicago,  Illinois 


Fig.  C4.     Emerson-Brantingham  Motor,  Showing  Governor 
Courteay  of  Emerson-Brantinoham  Company,  Rockfor/1.  Tlltnnix 

I 

retor.     This  bell-crank  lever  is  also  attached  by  linkage  to  a  dash 
pot  to  prevent  the  governor  from  "hunting/1  or  "surging."  as  it  is 


GASOLINE  TRACTORS  103 

variously  termed)  that  is,  fluctuating  violently  over  a  wide  speed 
range.  This  governor  is  designed  to  control  the  speed  of  the 
motor  between  a  minimum  and  a  maximum  of  400  to  700  r.p.m. 
and  is  adjustable  by  means  of  the  hand  lever  shown  in  Fig.  63, 
which  illustrates  the  combined  governor  and  magneto  unit  before 
attachment  to  the  motor. 

In  Fig.  64,  which  shows  the  complete  power  plant  of  the 
Emerson-Brantingham  12-20  tractor,  is  illustrated  another  type  of 
built-in  governor,  the  details  of  which  are  clearly  shown.  This 
governor  is  driven  by  a  belt  and  is  of  the  usual  steam-engine  type 
in  which  the  weights  are  carried  on  leaf  springs,  the  movement 
being  transmitted  to  the  throttle  through  the  linkage  shown. 

TRACTOR   CLUTCHES 

Functions  of  Clutches.  Since  the  internal  combustion  motor 
cannot  be  started  under  load  and  will  stall  if  the  load  be  applied 
too  suddenly,  even  though  the  engine  is  developing  its  full  power, 
it  is  necessary  to  employ  a  means  of  picking  up  the  load  gradually 
as  well  as  of  connecting  or  disconnecting  the  motor  from  the  load 
as  desired.  This  means  is  the  clutch;  and  clutch  problems  on  the 
tractor  are  the  same  in  kind  but  greater  in  degree  than  those 
encountered  on  the  automobile  since  the  load  to  be  started  is  so 
much  greater.  An  automobile  need  start  its  own  weight  only  and 
in  doing  so  it  encounters  but  slight  rolling  resistance,  whereas  the 
tractor  must  not  only  get  a  very  much  greater  weight  under  way 
but  in  starting  it  must  overcome  the  far  greater  resistance  repre- 
sented by  the  plows  or  other  load  and  also  that  of  the  ground 
itself,  . 

As  a  general  rule  the  types  of  clutches  employed  on  tractors 
are  the  same  as  those  used  on  automobiles,  but  they  are  given  a 
considerably  increased  area  of  contact  surfaces  and  these  surfaces 
are  held  together  under  much  higher  spring  pressures  in  order  to 
carry  the  heavier  load.  Regardless  of  its  type,  the  principle  of 
the  friction  clutch  is  based  upon  holding  the  driving  surface 
(directly  connected  to  the  motor)  and  the  driven  surface  (directly 
connected  to  the  transmission  or  speed  reduction  gear)  in  contact 
under  a  pressure  per  square  inch  that  is  greater  than  that  exerted 
by  the  engine  in  carrying  the  load.  When  the  pressure  required 


104  GASOLINE  TRACTORS 

to  carry  the  load  exceeds  that  exerted  by  the  clutch  spring,  the 
contact  surfaces  slide  upon  one  another  and  the  clutch  is  said  to 
slip.  Unless  this  slipping  took  place,  some  one  of  the  links  in  the 
transmission  between  the  wheels  or  tracks  and  the  engine  would 
have  to  give  way  or  the  engine  itself  would  be  stalled  by  the  load. 
It  is  accordingly  the  function  of  the  clutch  to  slip,  first,  to  insure 
gradual  engagement  in  picking  up  the  load  and,  second,  to  pre- 
vent damage  to  the  transmission  or  the  motor  when  the  load 
becomes  excessive.  The  latter  function,  however,  is  more  impor- 
tant in  theory  than  in  practice  since  an  excessive  load  almost 


Pig.  65.    Transmission  Unit  of  Illinois  Tractor  Showing  Multiple-Disc  Clutch 
Courtesy  of  Illinois  Tractor  Company,  Bloomington ,  Illinois 

invariably  stalls  the  motor  before  the  clutch  begins  to  slip,  unless 
its  surfaces  have  become  glazed  through  wear  or  its  spring  has 
weakened. 

Types  of  Clutches.  In  practically  every  case  the  flywheel  of 
the  motor  itself  forms  the  driving  member  of  the  clutch.  The 
driven  member  may  be  a  cone  faced  with  asbestos-wire  fabric,  a 
plate  faced  with  similar  friction  fabric,  or  a  contracting  band 
similarly  faced  which  is  mounted  so  as  to  contact  with  the  rim  of 
the  flywheel  itself  or  with  that  of  a  smaller  drum  attached  to  the 
flywheel;  or  friction-faced  shoes  may  be  arranged  to  expand 
against  the  inner  face  of  the  flywheel.  The  moving  force  in  every 
case  is  the  clutch  spring.  In  the  order  mentioned,  these  types  are 
known  as  the  cone,  plate,  contracting-band,  and  expanding-band, 


GASOLINE   TRACTORS 


105 


or  expanding-shoe,  clutches.  Where  a  greater  contact  area  is 
desired  than  is  afforded  by  the  diameter  of  the  flywheel,  a  series 
of  plates  or  discs  is  employed.  These  plates  are  divided  into  two 
groups,  one  of  which  is  carried  on  spindles  or  bolts  attached  to 


Fig.  66.     Section  of  Dry-Plate  Clutch  As  Used  on  Moline  Tractor 
Courtesy  of  Moline  Plow  Company,  Moline,  Illinois 

the  flywheel  and  forms  the  driving  member,  while  the  second 
group  is  similarly  mounted  on  members  attached  to  the  clutch 
shaft  and  forms  the  driven  member.  When  in  engagement,  the 
two  groups  are  pressed  together  by  the  clutch  spring  in  the  same 
manner  as  m  other  types  of  clutches.  This  clutch  is  known  as  the 


106 


GASOLINE   TRACTORS 


multiple-disc  type,  and  in  -....me  instances  it  operates  in  a  bath  of 
lubricating  oil,  the  latter  being  squeezed  from  between  the  plates 
as  they  come  in  contact,  thus  ensuring  gradual  engagement.  In 
Fig.  65  is  shown  the  multiple-disc  clutch  of  the  Illinois  tractor, 
the  clutch  being  the  small  group  of  plates  shown  at  one  end  of  the 
transmission  unit. 

Plate  Type.  The  sectional  diagram,  Fig.  66,  not  only  serves 
to  illustrate  the  details  of  the  dry-plate  clutch  but  also  makes 
clear  the  principles  of  clutch  operation.  This  is  the  Borg  and 
Beck  clutch  as  used  on  the  Moline  tractor.  One  of  the  asbestos 


Fitf.  <>7.     Main  Clutch  of  Holt  Caterpillar  Tractor 
Cniirtisi/  ,'f    Knit    MtnnifiK-tiirin'/  f'i>mj>fin>j,   Inc.,    Prorin,    Illinoix 

rings  shown  is  attached  to  the  flywheel,  while  the  second  ring  is 
carried  on  the  driven  clutch  member,  while  between  the  two  is  the 
clutch  disc,  which  is  a,  ring  or  disc  of  steel  also  attached  to  the 
clutch  shaft.  By  means  of  the  collar  and  toggle  levers  which  mul- 
tiply the  force  exerted  by  the  spring,  this  clutch  disc  is  clamped 
between  the  two  asbestos  rings  when  the  clutch  is  engaged.  The 
backward  pressure,  or  reaction  of  the  spring,  is  taken  on  the  hall 
thrust  bearing  shown,  this  being  an  essential  of  all  types  of  cone 
or  plate  clutches  since  otherwise  this  back  pressure  of  the  spring 
would  cause  considerable  frictional  resistance  to  the  revolution  of 


(1ASOL1XK    TRACTORS 


107 


the  clutch  shaft.  The  screw  marked  A  is  an  adjustment  to  main- 
tain the  distance  B  indicated,  this  distance  being  necessary  for 
the  complete  release  of  the  clutch  when  disengaged. 

Expanding-Shoe  Type.     The  Lauson  tractor  clutch  affords  an 
example  of  the   expanding-shoe  type   which   calls   for   very   little 


MOTOR    SUDE 
SPEED  CHANGS 


Fig.  68.     Friction  Transmission  of  Heider  Tractor 
Courtesy  of  Rock  Inland  Plow  Company,  Rock  Island,  Illinois 

explanation.  Against  the  inner  face  of  the  flywheel  are  two 
pivoted  shoes  which  are  counterbalanced.  These  shoes  are  faced 
with  asbestos  brake  lining  and  are  designed  to  be  held  in  contact 
with  the  inner  face  of  the  flywheel  rim  by  means  of  the  toggle 
mechanism  shown.  The  spring  has  the  same  location  as  in  other 


108  GASOLINE   TRACTORS 

types  of  clutches,  while  its  purpose,  like  that  of  other  clutches,  is 
to  hold  the  clutch  friction  surfaces  together  under  a  pressure 
greater  than  that  exerted  by  the  engine  in  driving  the  tractor 
under  load.  The  main  clutch  of  the  Holt  caterpillar  tractor  is  of 
a  similar  type,  Fig.  67. 

Contracting- Band  Clutch.  Neither  the  contracting-band  nor 
the  cone  clutch  calls  for  much  description.  The  contracting-band 
clutch  is  practically  a  duplicate  of  the  usual  brake  mechanism  in 
which  a  friction-lined  band  is  pressed  against  a  revolving  drum  to 
bring  the  latter  to  a  stop.  In  the  case  of  such  a  clutch  the  object 
is  to  bring  the  contracting  band  to  a  stop  on  the  drum,  which  is 


L  ^f 


Fig.  69.     Bevel  Friction  Transmission  of  Square  Turn  Tra<  tor 
Courtesy  of  Square  Turn  Tractor  Company,  Nor  foil:,  Xrl>ru»/.'<i 

the  flywheel,  so  that  both  the  band  and  the  flywheel  revolve 
together,  this  really  being  the  only  diiVerenee  between  the  brake 
and  the  clutch  mechanism.  The  contracting  band  is  ;:tt;>ched  to 
the  clutch  shaft,  or  driven  member,  and  when  in  operation, 
revolves  with  it,  thus  carrying  the  load.  This  clutch  is  rsed  in 
connection  with  a  planetary  type  of  transmission  and  is  accord- 
ingly familiar  through  its  employment  on  many  thousand  Fords. 
Cone  Clutch.  In  the  cone  clutch  the  inner  face  of  the  fly- 
wheel is  turned  to  a  bevel  of  approximately  ;>()  degrees  to  form 
the  driving  member  into  which  a  cone-shaped  member  with  the 
same  bevel  and  lined  with  asbestos  or  other  friction  facing  is 


GASOLINE   TRACTORS  109 

pressed  by  the  spring.  Owing  to  the  necessarily  limited  area  of 
friction  contact  in  this  type  of  clutch,  a  high  spring  pressure  is 
necessary  where  a  heavy  load  must  be  transmitted. 

On  the  automobile  this  spring  pressure  is  very  much  less  than 
on  the  tractor  owing  to  the  slight  resistance  encountered  by  the 
machine  in  starting,  so  that  the  clutch  may  readily  be  disengaged 
with  the  foot  through  the  medium  of  a  short  lever  and  pedal,  but 
on  any  tractor  except  a  very  light  one  the  effort  required  to  do 
this  would  be  excessive.  The  usual  method  of  clutch  operation  on 
the  tractor  is  accordingly  by  means  of  a  long  hand  lever  provided 
with  a  ratchet  or  locking  detent,  so  that  the  clutch  may  be  held 
out  of  engagement.  Since  it  does  not  benefit  the  spring  to  keep  it 
compressed,  the  clutch  should  not  be  locked  out  of  engagement 
any  longer  than  is  necessary  to  shift  the  transmission  gears  to 
neutral',  when  the  clutch  should  again  be  allowed  to  engage. 
Holding  the  clutch  out  of  engagement  overnight  or  while  the 
tractor  is  standing  in  the  field  subjects  the  clutch  spring  to  abuse 
and  will  soon 'result  in  weakening  it  to  the  point  where  the  clutch 
slips  whenever  any  extra  load  comes  on  it. 

Friction  Drive.  While  all  the  types  of  clutches  mentioned 
are,  in  a  sense,  a  friction  drive  in  that  friction  is  depended  upon 
to  transmit  the  power,  the  so-called  friction  drive  is  one  in  which 
the  load  transmitting  members  revolve  independently  of  one 
another  except  for  a  single  point,  or  line,  of  contact.  This  is 
made  clear  by  the  illustration  of  the  friction  transmission  of  the 
Heider  tractor,  Fig.  68.  The  flywheel  is  the  driving  member,  as 
usual,  but  in  this  case  its  entire  outer  rim  is  covered  with  a 
special  friction  facing  consisting  of  hard  fiber.  The  flywheel 
rotates  between  two  large  steel  discs,  either  one  of  which  may  be 
pressed  against  it.  In  this  instance  the  left-hand  disc  is  used  for 
forward  movement  and  the  right-hand  disc  for  backing,  or  reverse. 
It  is  also  apparent  that  the  point  at  which  the  flywheel  makes 
contact  with  the  disc  determines  the  speed  at  which  the  latter  and 
the  tractor  itself  are  driven. 

In  the  position  shown  the  tractor  speed  will  be  the  lowest 
provided,  since  the  flywheel  is  in  contact  with  the  outer  edge  of 
the  disc,  so  that  the  relation  of  the  two  is  that  of  a  small  gear  to 
a  large  one  and  the  speed  of  the  latter  is  reduced.  As  the  fly- 


110 


GASOLINE   TRACTORS 


wheel  moves  toward  the  center  of  the  driven  disc,  the  relationship 
between  the  two  becomes  that  of  driving  and  driven  gears  which 
approach  closer  and  closer  to  the  same  size,  so  that  the  speed  of 
the  driven  member  is  increased.  This  movement  of  the  flywheel 
is  accomplished  by  mounting  the  motor  itself  on  slides  on  the 
frame  and  moving  it  backward  or  forward  by  means  of  a  large 
hand  lever.  The  direction  of  movement  of  the  tractor  depends 
upon  which  disc  is  pressed  against  the  flywheel. 


Both  Wheels  Forward  Both  Wheels  Reversed  Left  Wheel  Forward  Left  Wheel  Reversed 


Right  Wheel  Forward 


Right  Wheel  Reversed         Right  Wheel  Forward —  Left  Wheel  Forward — 

Left  Wheel  Reversed  Rigel  Wheel  Reversed 

The  two  views  above  show  positions  of  Bevels  and 
Cones  in  making  quick  short  turn  either  direction 

Fig.  70.     Details  of  Operation  of  Bevel  Friction  Transmission 
Courtesy  of  Square  Turn  Tractor  Com  pun  a,  Xorfolk,   Xebraxl.u 

Bevel  Friction  Drive.  The  form  of  friction  drive  employed  on 
the  Square  Turn  tractor  is  shown  in  Fig.  69.  In  this  drive  the 
principle  is  exactly  the  same  as  already  outlined,  except  that 
friction-faced  (fiber)  conical  members  take  the  place  of  the  fly- 
wheel as  the  driving  member  and  corresponding  cones  of  iron  art 
the  driven  members.  The  design  is  also  modified  to  permit  of 
driving  either  rear  wheel  independently  or  both  in  different  direc- 
tions at  the  same  time  in  order  to  turn  short  corners.  The  small 
diagrams  showing  the  different  relations  in  which  the  driving  and 
driven  members  may  be  placed,  Fig.  70,  explain  the  operations 
much  better  than  a  description,  A  separate  hand  lever  controls 


GASOLINE   TRACTORS  111 

each  of  the  driven  discs,  or  traction  members.  Moving  both  of 
them  forward  drives  the  machine  ahead  through  both  driving 
wheels;  pulling  them  back  reverses  the  movement;  and  each  may 
be  used  independently,  so  that  one  drives  forward  while  the  other 
is  backing,  thus  turning  the  machine  as  if  on  a  pivot. 

TRACTOR   TRANSMISSIONS 

Speed  vs.  Weight.  The  power  generated  in  an  engine, 
whether  by  the  expansion  of  steam  or  that  of  the  ignited  gases  in 
an  oil  engine,  is  converted  into  mechanical  energy  by  applying  it 
to  the  movement  of  weight,  and  the  power  itself  is  represented  by 
the  extent  of  that  weight  and  the  number  of  times  per  minute 
that  it  is  moved.  Hence,  for  a  given  power  the  slower  the  speed 
at  which  the  engine  runs,  the  heavier  must  be  the  weight  moved 
since  it  is  set  into  movement  a  smaller  number  of  times  per  min- 
ute. By  increasing  the  speed,  or  number  of  impulses  per  minute, 
the  weight  moved  can  be  correspondingly  reduced.  This  fact 
explains  why  25  hp.  may  be  generated  by  a  single  cylinder  sta- 
tionary gas  engine  running  at  250  r.p.m.  or  by  a  four-cylinder 
motor  running  at  1000  r.p.m.  and  why  one  motor  is  scarcely  more 
than  one-eighth  the  size  of  the  other,  although  their  power  output 
is  the  same.  The  single  cylinder  engine  will  weigh  2  tons  or  more 
and  will  have  flywheels  of  large  diameter  weighing  more  than  the 
total  weight  of  the  smaller  engine,  but  both  move  the  same  amount 
of  weight  per  minute. 

Automobile  Practice.  On  the  automobile  the  object  of  the 
designer  is  to  keep  the  total  weight  down  as  much  as  possible  con- 
sistent with  reliability,  so  that  light  high-speed  motors  running  up 
to  2000  r.p.m.  or  higher  are  employed.  Such  motors  are  practical 
for  automobile  use  because  the  speed  ratio  between  the  driving 
and  driven  members — the  motor  and  the  rear  wheels— is  not 
excessive  despite  the  high  speed  of  the  motor. 

Tractor  Practice.  But  on  the  tractor,  where  the  maximum 
speed  in  plowing  cannot  exceed  three  miles  per  hour  and  is  pref- 
erably less  than  that  (2J  miles  per  hour  is  recommended  by  the 
Society  of  Automotive  Engineers  and  most  tractors  are  designed 
to  plow  at  2|  miles  per  hour),  the  higher  the  speed  of  the  motor, 
the  greater  the  number  of  steps  required  in  the  gear  reduction,  and 
each  step  represents  a  loss  of  power  in  friction  as  well  as  acldi- 


112  GASOLINE   TRACTORS 

tional  parts  to  wear  out.  Since  the  tractor  is  not  subject  to  the 
same  weight  limitations  as  the  automobile,  there  is  no  advantage 
in  employing  a  light  high-speed  motor.  Generally  speaking,  the 
slower  the  speed  of  the  motor  consistent  with  the  avoidance  of 
excessive  weight,  the  better  adapted  it  is  to  tractor  use.  The 
slow-speed  motor  running  at  450  to  7.10  r.p.m.  also  .has  the  further 
advantage  of  subjecting  its  moving  parts  to  less  rapid  wear  in 
service  and,  other  things  being  equal,  should  require  less  attention 
to  keep  in  satisfactory  running  condition. 

Function  of  Transmission.  In  the  section  on  tractor  motors 
it  has  been  pointed  out  that  the  types  in  general  use  belong  to 
two  distinct  classes:  those  which  have  developed  with  the  station- 
ary engine  as  a  basis;  and  those  that  are  an  outgrowth  of  auto- 
mobile practice.  In  either  case  the  engine  will  only  develop  its 
normal  rated  power  when  allowed  to  run  steadily  at  a  rate  close 
to  its  maximum  speed.  A  gear  reduction  must  accordingly  be 
interposed  between  the  motor  and  the  driving  members  of  the 
tractor;  the  speed  of  the  motor  determines  how  great  this  reduc- 
tion must  be,  while  the  space  and  the  limit  of  weight  available 
determine  what  form  it  will  take.  Whether  consisting  of  a  com- 
pact unit  such  as  is  used  on  the  automobile  or  of  large  pinions 
and  gears  occupying  the  entire  space  between  the  frame  members 
of  the  tractor,  this  speed  reducing  mechanism  is  usually  termed 
the  transmission.  This  name  includes  everything  between  the  clutch 
and  the  final  application  of  the  power  to  the  wheels  or  the  tracks, 
which  is  termed  the  final  drive. 

Wide  Range  of  Types.  Since  tractor  motors  differ  so  widely, 
there  is  naturally  a  correspondingly  wide  range  of  types  of  trans- 
missions, the  latter  varying  all  the  way  from  what  is  practically  a 
duplicate  of  the  gear  train  used  on  heavy  steam  tractors,  or  road 
rollers,  to  the  light  and  compact  gear  box  used  on  high-speed 
automobiles.  A  few  illustrations  of  typical  examples  of  each  class 
will  suffice  to  give  an  idea  of  how  widely  this  feature  of  the  trac- 
tor varies  on  different  designs.  In  comparing  these,  it  should  be 
borne  in  mind  that  while  increased  width  of  gear  face  affords  a 
larger  wearing  surface  to  carry  the  load  and  large  gear  diameter 
means  fewer  steps  in  the  reduction,  these  advantages  may  be  offset 
by  the  exposure  of  the  gears  to  dirt  and  mud. 


GASOLINE  TRACTORS  113 

The  great  differences  in  size  and  weight,  in  many  cases  where 
the  same  amount  of  power  is  to  be  transmitted,  are  accounted  for 
by  a  similarly  great  difference  in  the  character  of  the  materials 
used.  Small  pinions  and  gears  running  at  high  speeds  must  be 
made  of  alloy  steels,  hardened  and  toughened  by  heat  treatment, 
and  must  be  run  in  a  bath  of  oil.  Large  broad-faced  gears,  on 
the  other  hand,  may  be  made  of  steel  castings  or  even  cast  iron, 
and  it  is  the  usual  practice  to  run  them  to  a  great  extent  without 
protection. 

Speeds.  Since  the  speed  range  of  the  average  farm  tractor  is 
necessarily  very  low,  its  requirements  are  usually  covered  by  the 
provision  of  but  two  forward  speeds  and  one  reverse.  A  few 
machines  are  provided  with  three  speed  transmissions,  but  this  is 
the  exception  and  is  due  to  the  use  of  either  a  high-speed  motor 
or  an  automobile-type  transmission.  On  low  gear,  which  is  equiva- 
lent to  a  forward  speed  of  about  one  mile  per  hour,  the  speed 
reduction  between  the  motor  and  the  driving  wheels  of  the  tractor 
may  range  all  the  way  from  40-1  to  80-1,  that  is,  the  motor 
makes  80  revolutions  to  a  single  turn  of  the  driving  wheels  in  the 
second  case  mentioned.  Such  a  great  difference  between  the  motor 
speed  and  that  of  the  machine  itself  necessitates  a  number  of  gear 
reductions,  each  one  of  which  involves  a  power  loss  in  itself  and 
also  presents  an  extra  wearing  surface  that  needs  replacement 
sooner  or  later.  Generally  speaking,  the  lower  the  speed  of  the 
motor  consistent  with  the  avoidance  of  excessive  weight,  the  less 
loss  there  will  be  in  the  transmission  of  the  power  to  the  rear 
wheels  or  tracks,  as  the  case  may  be.  The  point  below  which  it 
does  not  pay  to  reduce  the  motor  speed  appears  to  line  between 
400  and  500  r.p.m.,  as  beyond  that  the  weight  increases  all  out  of 
proportion  to  the  advantage  gained,  while  the  upper  limit  lies 
between  700  and  800  r.p.m.;  that  is,  a  low-speed  motor  would 
govern  between  these  limits,  say  450  to  750  r.p.m.,  and  its  trans- 
mission would  be  designed  to  take  care  of  the  difference  between 
750  r.p.m.  and  the  number  of  turns  per  minute  made  by  the 
driving  wheels,  which  would  depend  upon  their  diameter. 

A  high-speed  motor,  on  the  other  hand,  would  run  at  1000  to 
1200  r.p.in.  and  its  power  would  fall  off  very  rapidly  the  moment 
its  speed  dropped  below  800  r.p.m.  To  avoid  an  excessive  number 


114 


GASOLINE  TRACTORS 


of  gear  reductions,  the  driving  wheels  of  a  tractor  equipped  with  a 
high-speed   motor   would   usually   be   made   comparatively   small, 


Fig.  71.     Friction  Drive  of  the  Port  Huron  12-25  H.P.  Farm  Tractor 
Courtesy  of  Port  Huron  Engine  and  Thresher  Company,  Port  Huron,  Michigan 


GASOLINE  TRACTORS 


115 


which  is  a  disadvantage  since  such  a  tractor  is  constantly  climbing 
the  grade  formed  by  its  small  wheels  sinking  into  soft  earth,  or 
depressions,  and  is-  accordingly  expending  a  large  fraction  of  its 


Fig.  72.     Plan  View  of  Avery  Transmission 
Courtesy  of  Avery  Company,  Peoria,  Illinois 

power  in  lifting  itself  rather  than  in  driving  ahead.  It  does  not 
necessarily  follow  that  a  tractor  equipped  with  a  high-speed  motor 
always  has  small  driving  wheels,  since  the  reduction  in  speed 
required  may  be  taken  care  of  in  the  final  drive. 


11(5 


(JASOLIXK    TRACTORS 


Heavy  Types.  Those  transmissions  which,  as  already  men- 
tioned, represent  a  continuance  of  the  practice  followed  for  years 
on  heavy  steam  tractors  and  road  rollers  are  known  as  heavy 
types.  Such  a  transmission  is  shown  in  Fig.  71,  which  gives  a  plan 
view  of  the  Port  Huron  12-25  friction-driven  tractor.  It  also 
affords  an  example  of  a  tractor  with  a  comparatively  high-speed 
engine  equipped  with  large  driving  wheels.  There  are  three  gear 
reductions  in  all:  the  first  will  be  noted  at  the  left;  the  second  is 
from  this  transverse  shaft  to  a  central  gear  on  a  shorter  transverse 
shaft  which  also  carries  two  small  pinions  meshing  with  the  hull 


Fig.  73.     Transmission  ana  Differential  ot  75  HP.  Tracklayer  Tractor 
Courtesy  of  C.  L.  Best  Gas  Tractor  Company,  San  Leandro,  California 

gears.  Ordinarily  the  bull  gears  are  attached  directly  to  the  driv- 
ing wheels,  but  in  that  location  it  is  difficult  to  protect  them, 
while  in  the  present  design  they  are  completely  encased. 

Since  a  tractor  must  make  very  short  turns  and  both  wheels 
must  be  driven  when  going  straight  ahead,  a  differential  is  indis- 
pensable. When  rounding  a  short  turn,  it  will  be  evident  that  the 
wheel  on  the.  outside  of  the  curve  must  travel  a  much  greater  dis- 
tance than  that  on  the  inside  and  that  if  both  were  driven  at  an 
equal  speed,  one  would  be  forced  to  slip  ami  impose  a  heavy 
^traiu  on  the  machine.  If  the  ground  condition  were  such  that 
the  wheel  would  not  slip,  rounding  the  turn  would  be  difficult. 


GASOLINE 


11 


In  the  Port  Huron  tractor  illustrated  the  differential  is  located  in 
the  second  transverse  shaft  which  carries  the  pinions  meshing  with 
the  bull  gears.  As  changes  in  speed  are  effected  through  the  fric- 
tion drive,  the  gears  of  this  transmission  are  constantly  in  mesh. 
The  A  very  transmission  shown  in  Fig.  72,  is  another  example 
of  the  heavy  type,  the  illustration  showing  the  relation  of  the 
horizontal  motor  to  the  transmission.  The  two  forward  speed 
redactions  are  represented  by  the  two  pinions  of  different  sizes 
carried  directly  on  the  crank-  v^,^  ,  ,  :_, 

shaft  of  the  motor,  while  the 
reverse  speed  is  the  pinion 
just  forward  of  these.  The 
transverse  shaft  just  under 
the  rear  end  of  the  motor 
embodies  the  differential  the 
1  lousing  of  which  will  be  noted 
at  the  right.  This  shaft  also 
carries  the  pinions  meshing 
with  the  bull  gears.  The  com- 
plete power  plant  is  carried  on 
a  sliding  frame,  and  the  differ- 
ent speed  changes  are  effected 
by  moving  the  motor  so  as  to 
bring  the  different  pinions  into 
mesh  with  the  large  gear  car- 
rying the  differential. 


Intermediate  Types.     Be- 


Fig.  74.     Cotta  Automobile  Transmissicn  of  Do£- 


Chit.-h  Type  As  Used  on  Four-Drive  Tractor 

Cinirtem/  of  Cotta  Transmission  Company, 

Roclcfjrd,  Illinois 


tween  the  heavy  types  just 
described  and  what  is  prac- 
tically a  motor-truck  transmission,  there  are  a  number  of  trans- 
missions that  conform  to  some  degree  with  automobile  gear-box 
practice  but  are  built  on  much  heavier  lines,  for  example,  the 
transmission  of  the  Best  75  hp.  tracklayer  type  tractor  shown  in 
Fig.  73.  Sliding  gears  are  employed  for  the  speed  changes,  and  a 
bevel  pinion  and  driving  gear  on  the  counter-shaft  which  incorpo- 
rates the  differential,  the  internal  bevel  gear  of  which  shows  plainly 
in  the  illustration.  A  typical  automobile-type  transmission  is  the 
Cotta,  Fig.  74,  as  used  on  the  Four  Drive  tractor. 


118 


GASOLINE  TRACTORS 


Fig.  75.     Transmission  and  Spring  Drive  Differential  of  10-30  Oil-Pull  Tractor 
Courtesy  of  Advance- Rumcly  Thresher  Company,  Inc.,  Laporte,  Indiana 


Fig.  76.     Transmission  of  Turner  Tractor 

Courtesy  of  Tunur  Manufacturing  Company,   Port   Washington, 
Wisconsin 


GASOLINE  TRACTORS 


119 


A  clearer  view  of  the  details  of  the  mechanism  of  a  differential 
is  shown  in  Fig.  75,  which  illustrates  the  Rumely  16-30  transmis- 
sion. One  of  the  features  of  this  differential  is  the  use  of  a  series 
of  eight  springs  for  taking  up  the  shock  of  starting  which  will  be 
noted  just  inside  the  large  gear.  Upon  engaging  the  clutch,  these 
springs  must  first  be  compressed  before  the  load  falls  upon  the  gear 
teeth,  thus  cushioning  the  latter.  Other  similar  transmissions  are 
the  Turner,  Fig.  76,  the  Hart-Parr,  Fig.  77,  and  the*  Nilson,  Fig.  78. 


Fig.  77.     Transmission  of  Hart-Parr  Tractor 
Courtesy  of  Hart-Parr  Company,  Charles  City,  Iowa 

Special  Types.  In  Fig.  79  is  shown  a  plan  view  of  the  trans- 
mission of  the  Twin  City  25-^45  tractor,  a  feature  of  which  is  the 
use  of  toothed,  or  clog,  clutches,  the  details  of  which  are  clearly 
shown.  This  view  also  shows  the  contracting-band  clutch  used  on 
this  machine.  The  dome  just  to  the  right  of  and  forward  of  the 
flywheel  houses  the  engine  governor.  Automobile  practice  is 
closely  approached  in  the  Yuba  transmission,  Fig.  80,  and  in  the 
Holt  caterpillar  transmission,  the  gear  box  of  the  10-ton  Holt 


TRANSMISSION 
CASE  COVER 


HIGHSPEED 
GEAR 


ROLLER 
BEARING 


T3IVING 
SPROCKET 


BRAKE  BAND    BRAKE  LfVCR 


HIGH-SPEED 

PINION 


BEVEL  GEAR 


GEAR-SHIFT 
QUADRANT 


BEVEL  PINION 


BUA 


Fig.  78.     Transmission  of  Nibon 

Courtesy  of  Nilson  Tractor  Com  pan;/ 


79.     Contrae^Bff-Bcad  Clutch  and  Transmission  of  Twin  Cit>  Tractor 

i if  Minneapolis  Stcd  anil  Ma-)iinrry  Company,  M inru'tipoli.t,  Minnesota 


J 


Fig.  80.     Dual  Automobile  Type  Transmission  of  Yuba  Tractor 
Courtesy  of  Yuba  Manufacturing  Company,  Mary^vUle,  California 


Fig.  81.     Transmission  of  10-Ton  Holt  Caterpillar 
Courtesy  of  Holt  Manufacturing  Company,  Inc.,  Peoria,  Illinois 


122 


GASOLINE   TRACTORS 


tractor  being  shown  in  Fig.  81.     Both  these  types  are  of  the  selec- 
tive  sliding-gear  type   generally   used   in   automobiles,   the   Yuba 


Fig.  82.     Worm  Drive  of  Sandusky  Tractor 
Courtesy  of  Dauch  Manufacturing  Company,  Sandusky,  Okie 


Fig.  83.    Tr:iMs:iii*.xi.>:i  of  Huber  Li^ht  Four  Tractor 
C'oiirti-xif  of  llulxr  Manufacturing  Company,  Marion,  Ohio 


transmission  clearly  showing  the  individual  clutches  which  are 
used  in  the  tracklaying  machine  to  enable  the  operator  to  drive 
either  track  separately  when  turning.  A  feature  taken  directly 


GASOLINE  TRACTORS 


123 


from  automobile  practice  is  the  use  of  the  worm  drive,  Fig.  82.  Tke 
Huber,  Fig.  83,  is  a  type  that  is  in  a  class  by  itself.  Its  details 
and  method  of  operation  are  clearly  indicated  in  the  illustration. 
Final  Drive.  As  in  the  case  of  the  automobile  there  is  a 
further  speed  reduction  between  the  engine  and  rear  wheels  in  the 
final  drive,  but  as  the  speed  reduction  between  the  tractor  engine 
and  its  driving  members,  whether  the  latter  be  wheels  or  tracks, 
is  so  great,  this  cannot  take  the  form  of  a  small  pair  of  bevel 


Fig.  84.     Sectional  View  of  Emerson-Brantingham  Company  Transmission,  Showing  Oil  Level 
Courtesy  of  Emerson-Brantingham  Company,  Roclcford,  Illinois 

gears.  The  usual  method  is  to  employ  bull  gears,  or  internal  gear 
rings  of  large  diameter  which  are  bolted  to  the  driving  wheels  and 
with  which  small  pinions  on  the  ends  of  the  transverse  shafts  of 
the  change-speed  gear  mesh.  In  some  instances  automobile  prac- 
tice is  followed  by  using  a  live  axle.  This  is  a  combination  of  a 
sliding  change-speed  gear  of  the  selective  type  with  a  planetary 
gear.  The  sectional  view  of  the  Emerson-Brantingham  transmission, 
Fig.  84,  clearly  shows  the  relation  of  the  selective  sliding  gears  and 
the  oil  level  necessary  for  lubrication. 


Fig.  85.     Details  of  Final  Drive,  or  Track  of  Holt  Caterpillar  Tractor 
Courtesy  of  Holt  Manufacturing  Company,  Inc.,  Peoria,  Illinois 


Fig.  86.     Final  Drive  of  C.  L.  Best  Tracklayer  Tractor 
Courtesy  of  C.  L.  Best  Gas  Tractor  Company,  San  Leandro,  California 


Fig.  87.    Details  of  Final  Drive  of  Yuba  Ball-Trend  Trartor 
Courtesy  of  Yuba  Jfanif/oefurfof  Company,  MarysrUte,  California 


GASOLINE  TRACTORS  125 

Final  drive  in  tracklaying  machines  is  usually  through  large 
sprockets  on  the  ends  of  the  transverse  shaft,  these  sprockets 
meshing  in  the  track  itself.  The  track  runs  on  rollers  or  balls 
and  passes  around  an  idler  at  the  end  of  the  tread,  this  idler 
being  made  adjustable  so  as  to  vary  the  tension  on  the  con- 
tinuous track.  The  details  of  the  Holt  caterpillar,  the  Best 
tracklayer,  and  the  Yuba  ball-tread  machines  of  this  type  are 
shown  in  Figs.  85,  86,  and  87,  which  make  the  principles  of 
operation  so  clear  that  further  explanation  is  unnecessary. 

Only  a  brief  mention  has  been  made  of  a  few  of  the  differ- 
ent types  of  transmissions  and  final  drives  employed  on  tractors, 
there  being  so  many  that  it  would  be  out  of  the  question  to 
attempt  to  describe  all  of  them,  particularly  since  not  a  few 
have  numerous  special  features.  The  foregoing  examples,  how- 
ever, cover  the  principles  employed  in  practically  all  tractor 
transmissions  and  suffice  to  make  clear  the  manner  in  which 
these  principles  are  applied. 

TRACTOR  OPERATION 

GENERAL   INSTRUCTIONS 

Tractors  Different  in  Design  but  Alike  in  Care  Required.     In 

the  foregoing  pages  an  attempt  has  been  made  to  outline  briefly 
the  principles  of  tractor  operation  with  just  sufficient  references 
to  actual  types  to  make  the  text  clear.  At  the  present  stage  of 
development  it  is  hardjy  possible  to  select  any  one  manufacturer's 
product  as  typical  of  tractor  design  in  general  or  as  embodying 
throughout  those  features  of  design  which  are  most  likely  to  become 
standardized  during  the  next  five  years  of  development.  There  are 
so  many  different  makes  on  the  market  and  frequently  so  many 
models  of  each  make  that  it  would  require  a  volume  larger  than  the 
present  one  merely  to  give  a  brief  description  of  all  of  them.  Con- 
sequently, no  extended  descriptions  of  any  tractors  are  given  here. 
While  designs  and  details  of  construction  differ  so  widely 
and  so  frequently,  all  oil  or  gas  engine  tractors  are  based  on 
certain  underlying  principles  and  all  call  for  the  same  kind  of 
care.  The  remainder  of  this  article  is  accordingly  devoted  to 
an  outline  of  the  methods  of  handling  tractors  in  service  with  a 


126  GASOLINE  TRACTORS 


view  to  pointing  out  clearly  just  the  kind  of  care  the  machine 
needs  to  keep  it  running  efficiently.  To  facilitate  reference,  this 
information  is  put  in  the  form  of  questions  and  answers  grouped 
under  the  particular  subjects  which  they  cover. 

Degree  of  Care  Necessary.  Before  taking  up  the  detailed 
consideration  of  tractor  operation  it  is  well  to  revert  for  a  moment 
to  the  comparison  between  the  automobile  and  the  tractor  in 
order  to  emphasize  the  great  difference  in  the  conditions  of  oper- 
ation of  the  two.  It  is  a  great  mistake  for  the  owner  or  operator 
of  a  tractor  to  conclude  that  because  he  can  keep  his  car  running 
for  weeks  at  a  time  and  subject  it  to  the  severest  kind  of  service 
without  being  called  upon  to  give  it  more  than  passing  atten- 
tion at  infrequent  intervals,  the  same  amount  of  care  will  suffice 
to  keep  the  tractor  running  equally  well.  The  most  severe 
service  to  which  an  automobile  can  be  subjected  is  trifling  com- 
pared to  what  a  tractor  must  undergo  in  plowing  ten  hours  a 
day.  No  comparison  between  the  two  is  possible.  The  atten- 
tion demanded  in  running  a  tractor  is  really  only  comparable  to 
that  required  by  a  marine  engine  which  is  run  steadily  at  full 
power. 

It  is  naturally  impracticable  to  employ  more  than  one  man 
to  run  the  average  tractor  so  that  the  single  operator  must 
assume  the  combined  tasks  of  the  oiler,  engine-room  attendant, 
and  engineer  on  watch  in  the  engine  room  of  a  steamer.  He 
must  see  that  every  part  is  constantly  lubricated,  must  watch 
all  moving  parts  in  sight  from  time  to  time  and  keep  all  his 
senses  on  the  alert  all  the  time  to  detect  the  first  indications  of 
overheating  or  faulty  operation  as  evidenced  by  the  sounds 
produced. 

Parts  Giving  Most  Trouble.  Over  two  thousand  tractor 
owners  sent  in  reports  in  answer  to  a  questionnaire  forwarded  to 
them  by  the  Department  of  Agriculture.  In  answer  to  the  ques- 
tion "What  part  of  your  tractor  gives  you  most  trouble?"  more 
than  seven  hundred  mentioned  some  part  of  the  motor  and  of 
that  number  considerably  over  one-half  gave  the  ignition  as  the 
chief  source  of  delay.  A  leading  tractor  manufacturer  substan- 
tiates this  by  stating  in  his  instruction  book  that  the  motor  is 
responsible  for  fully  75  per  cent  of  all  tractor  troubles  and  that 


GASOLINE  TRACTORS  127 

70   per    cent    of   the    motor   trouble    is    due    to    the    ignition.     A 
resume  of  the  answers  sent  in  to  the  questionnaire  follows: 

Magnetos  299  Cylinders  and  pistons  61 

Sparkplugs  110  Clutch  59 

Gears  108  Valves  and  springs  43 

Carburetor  104  Lubrication  29 

Bearings  80  Starting  28 

The  figures  given  in  each  case  represent  the  number  of  tractor 
owners  who  gave  the  part  in  question  as  the  chief  cause  of  their 
troubles  in  operation.  These  figures  do  not,  however,  give  any 
idea  of  the  relative  importance  of  the  parts  as  sources  of  trouble. 
Failure  of  the  magneto,  or  even  of  a  spark  plug,  brings  the 
tractor  to  a  halt,  but  the  trouble  may  usually  be  remedied  in  a 
very  short  time  and  no  damage  is  caused,  whereas  a  breakdown 
due  to  faulty  lubrication,  or  to  the  failure  of  the  cooling  system, 
which  is  not  mentioned  at  all,  will  usually  involve  the  loss  of 
anywhere  from  a  day  to  a  week  besides  a  heavy  repair  bill. 

Supply  of  Spares  Necessary.  The  cost  of  an  ample  supply 
of  spare  parts  is  small  compared  with  the  time  that  is  saved 
when  the  part  most  needed  is  right  at  hand  and  can  be  installed 
without  delay,  so  that  a  number  of  spares  of  the  most  necessary 
parts  should  be  considered  part  of  the  investment  and  be  bought 
at  the  same  time  as  the  machine.  Unless  it  be  an  ocean-going 
steamer,  there  is  hardly  another  piece  of  machinery  that  per- 
forms such  strenuous  service  so  far  from  a  repair  and  supply 
base  as  does  the  tractor.  It  would  be  just  as  foolish  for  the 
chief  engineer  of  a  steamer  to  leave  port  without  any  spare 
parts  in  the  storeroom  and  still  expect  to  arrive  at  his  destina- 
tion, regardless  of  what  happened,  as  it  is  for  a  farmer  to  pur- 
chase a  tractor  and  expect  to  get  through  his  first,  second,  or 
any  other  season  of  plowing  or  threshing  without  vexatious  delays 
unless  he  has  on  hand  spares  of  the  parts  most  frequently  needed. 

Manufacturer's  Service  Poor.  While  it  would  not  be  just  to 
generalize  by  saying  that  the  service  rendered  the  purchaser  by 
every  manufacturer  of  tractors  is  poor,  this  is  true  in  many  cases 
and  must  always  remain  so  for  the  farmer  who  is  located  miles 
from  the  nearest  dealer  representing  tbe  factory.  It  is  nothing 
unusual  to  waste  from  half  a  day  to  a  day,  telephoning  and 


128  (JASOLIXK    TRACTORS 

waiting  for  a  part  to  be  sent  out  or  driving  in  for  it.  The 
dealer  may  be  off  for  the  day  in  some  other  part  of  the  county, 
making  a  demonstration  or  closing  a  sale,  and  there  may  be  no 
one  in  his  place  of  business  to  render  the  desired  service.  Mean- 
while, the  machine  is  standing  idle.  There  are  few  replacements 
that  the  experienced  driver  of  a  tractor  cannot  make  without 
other  assistance  than  that  provided  by  the  usual  farm  shop,  so 
that  if  the  parts  are  on  hand  little  time  will  be  lost  in  getting 
the  machine  under  way  again. 

Parts  Needed.  While  the  make  of  the  tractor  in  question 
will  determine  the  character  of  many  of  the  spares  that  should 
be  carried  by  its  owner,  there  are  some  that  are  needed  with  all 
makes.  These  are  valves,  valve  springs,  and  small  parts  needed 
in  connection  with  the  valves,  igniters,  or  make-and-break  plugs 
for  low-tension  ignition  systems,  also  ignitor  trip  rods,  or  rather 
the  small  parts  which  compose  the  fittings  of  the  rod  rather  than 
the  rod  itself,  since  the  latter  is  not  subjected  to  wear.  Spare 
connecting  cables  cut  to  length  and  fitted  with  terminals,  whether 
for  high-  or  low-tension  systems,  will  often  be  found  valuable. 
Extra  fan  belts  and  spark  plugs  should  hardly  be  called  spare 
parts  in  this  connection  since  they  are  absolute  necessities  at 
comparatively  short  intervals.  Hose  connections  between  the 
motor  and  the  radiator  are  also  in  the  same  class.  Where  a 
motor  is  equipped  with  die-cast  main  bearings  or  connecting-rod 
bearings,  a  spare  set  will  often  prove  to  be  worth  many  times 
its  cost  in  the  saving  of  plowing  or  threshing  time,  since  even 
well-attended  machines  do  suffer  breakdowns  from  burnt-out  bear- 
ings at  times.  Extra  piston  rings  as  well  as  an  extra  piston 
and  a  connecting  rod  are  likely  to  be  called  for  sooner  or  later. 
The  magneto  is  a  pretty  expensive  piece  of  equipment  and,  more- 
over, it  is  usually  so  reliable  that  it  will  continue  to  work  season 
after  season  without  giving  any  trouble.  But  when  it  does  break 
down,  it  is  sometimes  beyond  the  ability  of  the  tractor  operator 
to  make  the  repair.  WThere  two  or  more  tractors  are  operated  on 
a  farm  and  the  same  magneto  is  standard  on  all  of  them,  it 
would  pay  to  invest  in  a  spaiv,  though  at  any  time  but  the 
height  of  the  season  the  laying  up  of  one  tractor  would  probably 
not  Oanse  anv  trouble. 


GASOLINE   TRACTORS  129 

The  foregoing  discussion  has  been  confined  to  enumerating 
motor  parts  or  accessories  that  should  be  carried  as  spares  since 
they  are  common  to  practically  all  motors.  So  far  as  the  rest 
of  the  machine  is  concerned,  the  owner  must  either  learn  from 
experience  what  parts  are  likely  to  wear  out  rapidly  and  need 
replacement  at  short  intervals,  or  he  must  depend  upon  the 
manufacturer's  representative  to  give  him  this  information. 
Naturally,  the  maker  and  his  salesmen  do  not  wish  to  give  the 
impression  that  any  of  the  machine's  parts  will  need  replacement 
in  a  short  time,  and  in  a  good  many  instances  they  are  as  much 
in  the  dark  as  the  purchaser  is,  since  it  may  be  that  the  model 
has  just  been  placed  on  the  market  and  there  has  been  no  oppor- 
tunity to  learn  its  weak  points  in  actual  service. 

Both  the  time  spent  in  getting  information  of  this  kind  and 
the  money  invested  in  the  necessary  spare  parts  will  return  very 
substantial  dividends  when  the  occasion  arises  to  use  the  parts. 
There  are  some  parts  that  may  never  be  used,  such  as  a  steering 
knuckle.  Get  the  manufacturer's  representative  to  give  you  a 
frank  opinion.  Point  out  your  position,  when  isolated,  and  do 
not  content  yourself  with  his  first  recommendations.  Insist  on 
finding  out  what  are  the  weak  parts  of  every  important  unit. 
The  factory  man  has  a  good  line  on  this  by  the  extent  of  the 
demand  for  certain  replacement  parts.  It  will  usually  be  found  a 
paying  investment  to  purchase  a  stock  of  almost  all  of  them 
rather  than  take  chances  on  getting  the  particular  part  most 
needed  at  a  time  when  the  tractor  is  worth  a  good  many  dollars 
an  hour  to  you. 

LUBRICATION 
MOTOR  LUBRICATION 

Q.  What  grade  of  lubricating  oil  should  be  used  for  a  slow= 
speed  tractor  motor;  for  a  high=speed  type? 

A.  Every  responsible  tractor  manufacturer  goes  to  consider- 
able expense  to  determine  just  what  grade  of  lubricating  oil  is 
best  adapted  to  his  own  engines.  His  investigation  covers  every- 
thing from  a  chemical  analysis  and  flash  test  of  every  grade  of 
oil  recommended  for  his  use  to  actual  tests  in  service  extending 
over  considerable  periods  of  time.  The  tractor  owner  should 


CASOLIM:  TRACTORS 

Accordingly  never  use  anything  l>nt  llie  oil  recommended  by  the 
manufacturer. 

Q.  In  a  motor  having  any  form  of  splash  lubrication,  that 
is,  one  in  which  part  of  the  supply  is  carried  in  the  crankcase 
pan,  how  often  should  the  oil  be  drained  from  the  crankcase? 

A.  The  recommendations  of  different  tractor  manufacturers 
range  all  the  way  from  every  day  to  once  in  two  weeks,  many 
giving  one  week  as  the  maximum  period  of  time  the  same  oil 
should  be  used. 

Q.  How  often  should  the  oil  in  a  circulating  system  be 
completely  replaced  with  a  fresh  supply? 

A.  It  should  he  repla.ee*  1  at  the  intervals  given  above  for  a,  splash 
system  since  the  service  demanded  of  the  lubricant  is  the  same. 

Q.  Does  oil  lose  its  lubricating  qualities  through  use,  and 
how  can  this  be  determined? 

A.  High  temperature  and  pressure  completely  change  the 
character  of  lubricating  oil  and  destroy  its  lubricating  qualities. 
The  lubricating  quality  of  an  oil  depends  upon  its  viscosity,  that 
is,  its  body,  upon  which  depends  its  ability  to  hold  apart  surfaces 
under  pressure  by  a  film  of  lubricant.  Dip  the  finger  ends  in 
some  old  oil  from  the  crankcase  and  rub  together  under  pressure. 
The  oil  will  have  a  thin  watery  feeling  and  the  finger  tips  may 
be  pressed  into  close  contact  through  it.  Try  the  same  experi- 
ment with  some  fresh  oil,  and  it  will  be  noted  that  a  sliding 
film  is  formed  between  the  fingers  despite  the  greatest  pressure 
that  can  be  put  upon  them  to  squec/e  it  out. 

Q.  What  influence  has  the  effect  of  high  temperature  and 
pressure  on  the  length  of  time  during  which  the  oil  should  be 
allowed  to  remain  in  the  crankcase? 

A.  Both  the  temperature  and  the  pressure  conditions  differ 
\\idely  in  different  engines  so  that  in  some  the  oil  literally  nrarx 
tmf  much  faster  than  in  others  and  should  accordingly  be  replaced 
oftener.  The  tractor  manufacturer  has  learned  from  experience 
the  proper  period  of  time  for  his  motors,  and  his  recommenda- 
tion is  based  on  a.  desire  to  avoid  having  his  customer  pay  for 
the  same  experience. 

Q.  Next  to  labor  and  fuel,  lubricating  oil  is  the  most 
expensive  item  of  tractor  maintenance.  Is  it  really  economy  to 


GASOLINE   TRACTORS  131 

replace   what   appears   to    be   good   oil   as   often   as   the    tractor 
manufacturer  recommends  it? 

A.  The  cost  of  repairs  due  to  a  single  breakdown  from 
failure  of  the  lubrication  would  usually  buy  anywhere  from  one 
to  five  or  more  50-gallon  barrels  of  oil,  without  taking  into 
account  the  loss  of  time  due  to  the  tractor  being  out  of  service. 
It  is  the  highest  form  of  economy  to  follow  the  maker's  instruc- 
tions in  this  respect;  if  these  are  to  discard  the  oil  at  the  end 
of  every  day's  service,  it  will  be  found  far  cheaper  in  the  end  to 
do  so.  Many  tractor  owners  do  not  regard  it  as  necessary  to 
clean  out  the  crankcase  more  than  once  or  twice  a  season,  but 
instead  of  saving  oil  they  are  simply  running  up  repair  bills. 

Q.  What  other  causes  tend  to  destroy  the  lubricating  quality 
of  the  oil? 

A.  Another  cause  is  leakage  of  the  fuel  past  the  pistons  so 
that  the  supply  of  oil  in  the  crankcase  is  thinned  out  by  the 
gasoline  or  kerosene.  This  is  particularly  true  of  kerosene,  espe- 
cially if  the  motor  be  run  at  a  low  temperature  so  that  the  kero- 
sene vapor  condenses  into  a  liquid.  The  admixture  of  carbon  and 
dirt  with  the  oil  also  tends  to  destroy  its  lubricating  quality. 
Compare  the  color  of  oil  that  has  been  used  for  some  time  with 
fresh  oil;  the  difference  is  due  entirely  to  the  foreign  matter  that 
has  become  mixed  with  it. 

Q.     What  attention  does  a  force=feed  lubricator  require? 

A.  The  sight  feeds  should  be  watched  frequently  to  note 
whether  oil  is  constantly  passing  through  them  or  not.  To  make 
certain  of  this,  dirt  should  be  wiped  from  the  glasses  at  least 
once  a  day.  While  this  type  of  lubrication  has  the  great  advan- 
tage of  constantly  feeding  fresh  oil  to  the  bearings  almost  as  fast 
as  it  is  consumed,  its  factor  of  safety  is  not  so  high  as  that  of 
the  splash  or  circulating  type.  In  other  words,  failure  of  the 
part  is  apt  to  follow  immediately  upon  a  stopping  of  the  feed 
since  it  usually  receives  no  lubrication  from  any  other  source. 
The  lubricator  must  accordingly  be  watched  closely  and  the 
engine  stopped  at  once  if  any  of  the  feeds  has  become  clogged. 

Q.     How  often  should  such  a  lubricator  be  supplied  with  fresh  oil? 

A.  The  maker's  instructions  may  be  followed  but  a  still 
better  practice  is  to  get  into  the  habit  of  keeping  the  lubricator 


(1ASOLINK   TRACTORS 

constantly  filled;  that  is,  of  filling  it  twice  or  oftener  a  day,  if 
necessary,  rather  than  waiting  until  the  supply  runs  low.  A 
gage  glass  on  the  side  of  the  lubricator  shows  the  amount  in  it. 
The  plunder  pumps  which  force  the  oil  to  the  bearings  will 
always  work  better  when  there  is  an  ample  supply. 

Q.  What  other  precautions  should  be  taken  with  a  force= 
feed  lubricator? 

A.  When  it  is  driven  by  a  belt,  close  watch  should  be  kept 
on  the  belt  to  see  that  it  does  not  become  too  loose,  since  any 
slackening  of  the  belt  slows  down  the  pumps  and  supplies  less 
oil  to  the  bearings. 

Q.     How  often  should  a  force=feed  lubricator  be  cleaned  out? 

A.  Two  or  three  times  a  season  should  ordinarily  be  ample, 
but  this  will  depend  to  some  extent  upon  the  care  that  is  exer- 
cised in  handling  the  supply  of  oil  itself.  Unless  the  oil  supply 
is  kept  in  a  covered  oil  tank,  more  or  less  dust  and  other  foreign 
matter  is  bound  to  find  its  way  into  it.  The  presence  of  dirt 
in  the  oil  will  make  itself  apparent  by  clouding  the  inside  of  the 
sight-feed  glasses,  making  them  difficult  to  read.  Oil  having 
visible  foreign  matter,  such  as  small  specks  of  grit,  short  ends  of 
straw,  or  chaff,  in  it  should  never  be  put  into  the  lubricator 
without  straining,  as  it  is  liable  to  clog  the  pump  valves. 

Q.     How  is  a  force=feed  lubricator  cleaned  out? 

A.  By  disconnecting  the  leads  and  flushing  it  out  thoroughly 
\vith  gasoline  or  kerosene.  The  leads  should  be  disconnected  at 
both  ends  and  also  flushed  out,  blowing  through  them  to  see 
that  they  are  clear  from  end  to  end. 

Q.     Are  some  of  these  leads  more  apt  to  clog  up  than  others? 

A.  Those  that  supply  oil  to  the  pistons  are  most  likely  to 
clog  owing  to  an  accumulation  of  carbon  in  the  ends  opening 
into  the  cylinder.  They  should  be  taken  off  at  shorter  intervals 
and  all  carbon  removed  in  the  tube  itself  as  well  as  in  the  open- 
ing through  which  the  oil  passes  through  the  cylinder  wall. 

Q.    What  attention  does  a  circulating  system  require? 

A.  A  circulating  system  requires  replenishing  of  the  entire 
supply  after  washing  out  at  intervals,  as  directed  in  the  manu- 
facturer's instructions;  examination  at  short  intervals  of  the  oil 
pump;  and  l'iv<|iiriit  washing  oil'  of  the  oil  pump  screen.  Keep 


GASOLINE   TRACTORS  133 

the  sight-feed  glasses  clean  and  shut  down  immediately  if  an  oil 
stream  fails  to  appear  in  any  of  them  (some  tractors  have  but 
one,  others  several). 

Q.  What  general  precautions  should  be  observed  in  clean= 
ing  out  a  lubricating  system  of  any  type  and  in  handling  oil? 

A.  Always  avoid  the  use  of  waste  or  rags  from  which  lint 
will  detach  itself  in  wiping  out  the  crankcase  or  any  part  of  the 
system,  since  these  threads  will  invariably  clog  an  oil  pump  or 
feeder  tubes.  All  cans  or  other  vessels  used  in  handling  oil  should 
be  kept  covered  to  prevent  dust  falling  in  them  and  should  be 
wiped  clean  before  using.  Dust  is  simply  fine  grit,  and  its  pres- 
ence in  the  oil  converts  it  into  a  grinding  compound  which  will 
quickly  cut  away  bearing  surfaces. 

Q.     What  other  lubrication  does  the  motor  require? 

A.  This  will  depend  entirely  on  the  type  of  motor.  Where 
it  has  overhead  valves  as  used  on  many  tractor  motors,  the  rocker 
arm  spindles  and  pin  should  be  oiled  at  least  once  or  twice  a 
day  with  a  hand  oiler.  This  applies  as  well  to  any  other  external 
moving  parts  not  lubricated  by  the  oiling  system  of  the  motor. 
The  grease  cups  on  the  fan  and  on  the  pump  should  be  turned 
down  at  least  once  a  day.  Some  tractors  are  equipped  with 
gravity  oilers  for  this  purpose. 

CONTROL  SYSTEM    LUBRICATION 

Q.     How  is  the  clutch  lubricated? 

A.  On  some  tractors  it  is  enclosed  in  the  same  housing  as 
the  motor  and  runs  in  a  bath  of  oil.  Where  it  is  not  housed  in, 
grease  cups  are  usually  provided  on  the  clutch,  and  these  should 
be  turned  down  at  least  once  a  day.  Xo  oil  should  be  allowed 
to  fall  on  the  facing,  as  this  would  reduce  the  holding  power,  of 
the  clutch  and  cause  it  to  slip. 

Q.  What  attention  is  required  to  keep  the  transmission 
properly  lubricated? 

A.  When  the  transmission  is  of  the  enclosed  type,  running 
in  oil,  it  should  be  kept  filled  to  the  height  given  in  the  maker's 
instructions  and  with  the  grade  of  lubricant  recommended.  Don't 
attempt  to  use  cup  grease,  or  a  home-made  compound  of  grease 
and  oil  or  graphite,  as  the  different  materials  will  separate,  nor 


134  GASOLINE   TRACTORS 

should  heavy  steam  cylinder  oil  be  used,  since  it  contains  animal 
fats  and  will  become  acid,  attacking  the  steel  faces  of  the  gears. 
The  pressure  between  the  gear  teeth  in  a  transmission  is  very 
high  so  that  the  oil  wears  out  in  time  and  should  be  replaced  at 
intervals  of  two  to  three  months.  Watch  the  transmission  hous- 
ing for  leaks  and  renew  felt  washers  or  other  provision  for  pre- 
venting leaks. 

Q.     How  are  open  transmission  gears  lubricated? 

A.  Where  gears  are  run  without  a  housing,  they  are  not 
intended  to  be  lubricated  and  care  should  be  taken  to  see  that 
no  oil  or  grease*  gets  on  them  as  it  will  hold  dirt  and  grit  and 
cause  the  teeth  to  wear  out  much  faster.  The  gears  should  be 
kept  free  of  mud  and  dirt,  but  an  oily  rag  or  waste  should  never 
be  used  for  this  purpose.  This  also  applies  to  the  bull  pinion 
and  gear  except  where  completely  housed  in. 

Q.  What  attention  is  required  to  lubricate  other  moving 
parts  of  the  tractor? 

A.  Grease  cups  are  usually  provided  on  all  other  moving 
parts,  and  they  should  be  turned  down  as  instructed  by  the 
maker.  In  some  instances  the  directions  are  to  screw  these  cups 
down  as  often  as  twice  a  day;  in  others,  once  an  hour. 

ENGINE   PARTS 
ENGINE    BEARINGS 

Q.  How  long  will  motor  bearings  run  without  developing 
sufficient  play  to  require  adjustment? 

A.  This  will  depend  largely  upon  the  motor  itself  and  the 
service  demanded  of  the  tractor.  If  it  is  being  run  constantly 
with  an  overload,  they  will  need  attention  much  sooner  than 
when  the  machine  is  not  called  upon  to  carry  more  than  75  per 
cent  of  its  load  for  the  greater  part  of  the  time.  In  any  case 
the  bearings  should  be  examined  at  least  once  a  week;  some 
makers  recommend  that  they  be  tested  for  looseness  as  often  as 
twice  a  week  when  in  constant  service. 

Q*    How  can  the  bearings  be  tested  for  looseness? 

A.  They  should  always  be  examined  just  after  the  motor 
has  been  shut  down  and  is  still  hot;  the  amount  of  play  will  be 


GASOLINE   TRACTORS  135 

greater  when  all  the  parts  are  cold  but  some  of  this  will  be  taken 
up  by  the  thickened  oil  film  then  present  and  their  condition 
cannot  be  determined  as  satisfactorily.  The  connecting-rod  bear- 
ings are  the  first  to  show  signs  of  looseness.  Take  the  handhole 
covers  off  the  crankcase  and  turn  the  motor  until  two  of  the 
connecting-rod  ends  are  close  to  the  openings.  If  there  is  much 
play,  it  will  be  evident  upon  grasping  the  connecting  rod  and 
attempting  to  lift  it,  but  this  amount  would  usually  cause  a 
knock  in  operation.  Take  a  small  bar  and  pry  the  bearing 
upward  from  below,  keeping  the  other  hand  on  the  rod  to  detect 
any  movement.  Do  not  confuse  the  side  play  of  the  bearing 
with  looseness  of  the  bearing  itself  as  a  small  amount  of  side 
movement  is  allowed  on  all  connecting-rod  bearings.  Apply  this 
test  to  the  other  two  connecting  rods  also.  A  bar  may  also  be 
used  to  detect  any  looseness  of  the  main  or  crankshaft  bearings. 

Q.  Will  it  do  any  harm  to  allow  a  certain  amount  of  play 
in  these  bearings? 

A.  Nothing  will  be  apt  to  run  up  a  big  repair  bill  quicker 
than  running  the  motor  with  the  bearings  too  loose.  Every 
reversal  of  movement  pounds  the  crankshaft  and  in  time  will 
cause  crystallization  of  the  steel  with  consequent  breakage  of  the 
shaft.  The  resulting  vibration  is  also  detrimental  to  every  other 
part  of  the  motor. 

Q.  How  are  the  bearings  adjusted  when  a  test  reveals 
play  in  them? 

A.  Most  motor  bearings  are  provided  with  shims,  that  is, 
small  strips  of  metal  placed  between  the  halves  of  the  bearing 
and  through  which  the  bolts  pass  to  hold  the  bearing  together. 
Take  off  one  or  more  shims  on  each  side  of  the  bearing  and 
screw  down  the  nuts  again  tightly.  To  obtain  a  proper  adjust- 
ment, you  must  be  able  to  set  up  these  nuts  as  far  as  they  will 
go  without  binding  the  shaft.  Open  the  pet  cocks  or  the  com- 
pression release,  where  one  is  provided  on  the  engine,  and  try 
the  adjustment  by  cranking  the  motor  by  hand.  It  will  be  very 
difficult  to  turn  the  motor  over  if  the  bearings  are  too  tight. 
They  should  be  adjusted  so  that  the  motor  turns  easily,  indi- 
cating that  there  is  sufficient  space  between  the  bearing  halves 
and  the  shaft  to  permit  the  formation  of  an  oil  film  between 


130  (1ASOUNK    TRACTORS 

them.  The  shaft  should  be  tested  for  play,  as  already  described, 
to  prevent  making  the  adjustment  too  loose. 

Q.  When  a  bearing  is  too  tight,  is  it  good  practice  to  ease 
off  the  nuts  and  let  the  shaft  run  that  way? 

A.  A  bearing  is  not  properly  adjusted  unless  the  nuts  can 
be  set  up  hard  on  the  bearing  caps,  all  adjustments  being  made 
by  removing  or  re-inserting  shims,  or  laminations  of  metal  only  a 
few  thousandths  of  an  inch  thick.  One  or  two  shims  should  be 
removed  from  each  side  at  a  time  and  the  adjustment  tested. 
Care  must  always  be  taken  to  see  that  the  bearing  cap  is  replaced 
on  the  bearing  from  which  it  was  taken  and  that  it  is  put  back- 
in  ihe  same  way. 

Q.  Is  it  ever  necessary  to  adjust  the  piston=pin,  or  wrist= 
pin,  bearing? 

A.  This  is  the  bearing  which  holds  the  upper  end  of  the 
connecting  rod  in  the  piston  and  if  the  motor  is  properly  lubri- 
cated with  clean  oil,  it  will  seldom  require  any  attention.  In 
some  motors  the  pin  is  held  fast  in  the  sides  of  the  piston  and 
the  connecting  rod  moves  on  it,  and  shims  are  provided  on  the 
connecting-rod  bearing  for  adjustment.  In  others  the  upper  end 
of  the  connecting  rod  is  clamped  fast  to  the  pin,  and  the  pin 
moves  in  bronze  bushings  in  the  sides  of  the  piston  or  bears 
directly  on  the  piston  walls.  Allowing  the  big-end  connecting- 
rod  bearings  and  the  crankshaft  bearings  to  become  too  loose  so 
that  the  motor  knocks  is  the  chief  cause  of  lost  motion  in  the 
wrist-pin  bearing.  Where  the  pin  bears  in  the  piston  walls  this 
may  wear  the  holes  out  of  round  so  that  they  have  to  be  rebored 
and  bushed  to  make  a  good  bearing. 

Q.  When  the  connecting  rod  or  crankshaft  bearings  of  a 
motor  require  adjustment  at  frequent  intervals,  what  is  the  cause 
of  the  trouble? 

A.  The  cause  is  faulty  lubrication:  failure  to  clean  out  the 
crankcase  at  the  proper  intervals,  with  the  result  that  the  oil 
loses  its  lubricating  qualities  and  the  dirt  that  becomes  mixed 
with  it  cuts  away  the  bearing  surfaces. 

Q.  Where  bearings  have  become  worn  to  the  point  where  it  is 
no  longer  possible  to  adjust  them  properly,  is  it  practical  for  the 
average  operator  of  a  tractor  to  replace  them  with  new  bearings? 


GASOLINE  TRACTORS  137 

A.  It  is  not  practical  unless  he  has  had  experience  in  the 
work,  since  it  requires  accurate  lining  up  and  scraping  in  of  the 
bearings  to  a  close  fit.  Unless  this  is  carried  out  properly,  such 
heavy  stresses  will  be  imposed  on  the  crankshaft  that  it  will 
break  sooner  or  later.  Therefore  it  is  poor  economy  to  attempt 
this  repair  without  actually  having  had  experience  in  making  it; 
it  is  one  of  those ;  things  that  cannot  be  learned  from  an  instruc- 
tion book.  It  is  necessary  to  see  it  clone  in  the  shop  more  than 
once  and  the  first  attempt  should  be  made  under  the  supervision 
of  one  who  has  had  experience. 

VALVES 

Q.  What  attention  is  required  to  keep  the  valves  in  good 
operating  condition? 

A.  The  valve  stems  must  be  lubricated  one  or  more  times 
a  day,  except  on  motors  provided  with  special  means  for  doing 
this  automatically.  The  clearance  between  the  valve  tappet  and 
push  rod,  or  between  the  end  of  the  rocker  arm  and  the  valve 
stem,  depending  upon  the  type  of  motor,  must  be  adjusted  at 
frequent  intervals  and  the  valves  themselves  must  be  ground  as 
often  as  is  necessary  to  keep  them  tight. 

Q.  Why  is  adjustment  of  the  clearance  necessary,  and 
what  should  this  be? 

A.  The  constant  hammering  of  the  tappet  or  rocker  arm 
against  the  valve  stem  tends  to  increase  this  clearance  as  well  as 
to  wear  away  the  parts,  thus  increasing  the  distance.  The  greater 
this  distance  is  the  less  the  valve  will  lift  when  operated,  so  that 
less  fuel  is  admitted  on  the  intake  stroke  and  some  of  the  exhaust 
gases  are  left  in  the  cylinder  on  the  exhaust  stroke,  thus  cutting 
down  the  power.  This  clearance  should  be  just  sufficient  to 
allow  the  valve  to  close  completely  under  the  pull  of  its  spring 
when  the  tappet  or  rocker  arm  is  released  by  the  cam.  It  should 
be  tested  and  adjusted  with  the  motor  hot,  since,  if  made  very 
close  when  cold,  the  expansion  of  the  parts  is  apt  to  prevent 
the  valve  from  closing  properly.  An  ordinary  visiting  card  or  a 
piece  of  tin  plate  makes  a  good  gage;  it  should  be  possible  to 
slip  this  between  the  tappet  and  stem  easily.  In  any  case  the 
clearance  should  not  exceed  ^V  inch. 


138  GASOLINE  TRACTORS 

Q.     How  often  should  the  valves  be  ground? 

A.  When  a  tractor  is  being  used  ten  hours  a  day  and  six 
days  a  week,  they  will  doubtless  require  grinding  once  every  four 
to  six  weeks,  depending  more  or  less  on  the  motor  itself;  some 
motors  run  very  much  hotter  than  others  and  in  some  the  pro- 
vision for  cooling  the  exhaust  valve  is  inadequate,  so  that  more 
frequent  attention  is  necessary. 

Q.  How  may  the  valves  be  tested  for  leakage  without 
taking  the  motor  down? 

A.  Turn  the  motor  over  by  hand  about  one-third  of  a  revo- 
lution, until  two  of  the  pistons  are  within  an  inch  or  two  of  the 
upper  dead  center.  At  this  point  the  pressure  in  the  cylinder 
that  is  then  on  the  compression  stroke  should  be  highest.  Hold 
the  piston  up  against  this  pressure,  just  exerting  sufficient  pull 
to  cause  the  piston  to  move  if  the  compression  leaks  away.  In 
a  motor  that  is  in  good  condition,  there  should  be  no  perceptible 
movement  due  to  leakage  in  the  course  of  two  or  three  minutes, 
and  if  the  pull  of  the  hand  is  slackened,  the  piston  should  tend 
to  push  the  starting  crank  down  again  under  the  influence  of 
the  pressure  in  the  cylinder.  Apply  the  test  to  each  cylinder  in 
turn  and  any  difference  in  the  compression-holding  power  of  the 
different  cylinders  will  be  noticeable. 

Q.  When  the  usual  adjustment  of  the  clearance  does  not 
correct  a  loose  and  noisy  valve  action,  what  is  apt  to  be  the 
cause  of  the  trouble? 

A.  The  pin  of  the  cam  roller  has  probably  worn  so  that 
there  is  considerable  lost  motion  between  the  roller  and  the  pin 
on  which  it  turns.  The  only  remedy  is  to  replace  the  roller 
and  pin  or  maybe  the  tappet  complete.  Any  lost  motion  at 
this  point  permits  the  roller  to  move  upward  the  distance  repre- 
sented by  the  wear  before  the  tappet  itself  can  lift.  While  the 
play  at  any  one  point  may  be  very  small,  when  it  is  increased 
by  an  equivalent  amount  at  two  or  three  other  points,  the  total 
is  sufficient  to  reduce  the  effective  valve  opening  considerably, 
with  a  corresponding  decrease  in  the  power.  When  new  parts 
are  not  readily  obtainable,  this  condition  may  be  remedied  by 
boring  out  the  holes  of  the  cam  roller  and  the  rocker  lever  and 
fitting  them  with  bushings. 


GASOLINE  TRACTORS  139 

Q.  When  grinding  valves,  is  it  necessary  to  continue  the 
operation  until  the  entire  valve  and  seat  have  taken  on  a  polish? 

A.  No;  the  operation  may  be  considered  complete  when 
both  the  valve  and  the  seat  are  smooth  all  around  and  com- 
pletely free  from  any  sign  of  pitting.  A  polished  surface  may 
give  a  little  closer  fit,  but  the  difference  is  not  enough  to  com- 
pensate for  the  time  necessary  to  produce  it.  The  grinding 
operation  should  always  be  finished  by  the  use  of  the  fine  grind- 
ing compound. 

Q.  In  case  a  motor  has  been  allowed  to  run  until  the  valve 
seats  have  become  very  badly  pitted,  is  it  necessary  to  cut  these 
down  by  grinding  alone? 

A.  No;  a  valve-seat  reaming  tool  should  be  employed  for 
cutting  away  the  metal  until  the  pitting  has  almost  disappeared, 
and  the  remainder  of  the  operation  should  then  be  carried  out 
by  grinding  in  the  usual  manner.  No  more  metal  than  necessary 
should  be  removed  with  the  reamer  as  cutting  too  deep  will 
simply  shorten  the  life  of  the  cylinder  casting.  Valves  are  made 
in  two  standard  tapers,  45  degrees  and  60  degrees,  and  care 
must  be  taken  to  see  that  the  angle  of  the  reamer  blades  corre- 
sponds to  that  of  the  valve  seat  before  beginning  to  cut. 

Q.  Is  there  any  way  of  testing  the  tightness  of  the  valves 
before  putting  them  back  into  the  motor? 

A.  When  the  valves  are  in  cages,  they  may  be  tested  by 
pouring  some  gasoline  into  the  cage  and  noting  whether  it  leaks 
past  the  valve  or  not. 

Q.  Does  a  rapid  loss  of  compression  under  such  a  test 
always  definitely  indicate  that  the  valves  are  at  fault? 

A.  No;  the  piston  rings  may  be  worn  or  the  lubrication 
may  be  *poor,  so  that  there  is  not  a  good  compression  seal  in 
the  cylinder.  To  definitely  ascertain  the  trouble,  take  out  the 
spark  plugs  and  pour  an  ounce  or  two  of  heavy  cylinder  oil  into 
each  cylinder.  Turn  the  motor  over  fifteen  to  twenty  times 
with  the  plugs  out  to  work  this  oil  down  on  the  pistons,  replace 
the  spark  plugs  and  repeat  the  test  as  first  described.  Failure 
to  hold  compression  will  then  mean  poorly  seating  valves  almost 
invariably,  since,  with  a  fresh  oil  seal,  even  loose  piston  rings 
will  hold  compression  when  the  motor  is  being  turned  over  by 


110  (iASOLiXK   TRACTORS 

liaiul.  The  necessity  For  putting  in  lliis  oil  indicates  that  the 
oil  in  the  crankcase  or  the  circulating  system  needs  renewing. 
This  test  for  loss  of  compression  should  be  carried  out  with  the 
motor  cold. 

Q.    What  is  the  best  method  of  grinding  the  valves? 

A.  With  a  valve-in-head  type  of  motor,  take  the  valve 
cages  over  to  the  bench  so  that  there  is  no  risk  of  getting  any  of 
the  grinding  compound  into  the  cylinders.  Use  nothing  but  the 
specially  prepared  grinding  compound  designed  for  this  purpose; 
ordinary  emery  and  oil  should  never  be  employed  as  it  will  score 
the  valve  and  its  seat.  When  a  special  valve  grinder  is  not  at 
hand,  a  screw  driver  bit  in  an  ordinary  brace  makes  the  best 
grinding  tool.  Smear  some  of  the  compound  on  the  valve,  drop  it 
on  its  seat  and  turn  it  first  one  way  and  then  the  other,  making 
about  a  quarter  turn  in  each  direction  without  exerting  much 
pressure.  When  the  compound  has  been  squeezed  out,  put  in 
more  and  continue  the  operation,  repeating  this  for  fifteen  to 
twenty  minutes.  Wash  the  valve  and  seat  off  with  kerosene  and 
examine  to  see  if  all  signs  of  pitting  have  been  removed  and  the 
valve  has  a  bright  uniform  band  around  its  entire  circumference. 
The  presence  of  any  breaks  in  this  ring  indicates  low  spots  and 
calls  for  further  grinding.  Never  turn  the  valve  completely 
around  when  grinding,  making  only  a  quarter  turn,  since  the  com- 
plete turn  will  score  the  seat.  Be  careful  to  flush  off  every  trace 
of  the  grinding  compound  with  kerosene  when  through  to  pit* vent 
any  trace  of  it  getting  into  the  cylinder.  Otherwise,  the  engine 
will  be  ruined.  Where  the  valves  cannot  be  taken  away  from  the 
motor  for  grinding,  the  greatest  care  must  be  exercised  to  prevent 
any  of  the  compound  from  getting  into  the  cylinders  or  down  into 
the  valve  guides. 

Q.  Why  is  it  necessary  to  grind  the  valves  at  such  short 
intervals? 

A.  The  exhaust  valves  in  particular  are  subjected  to  exceed- 
ingly high  temperatures  that  pit  the  metal  Face  of  the  valve. 
Once  this  pitting  starts,  it  proceeds  rapidly  and  if  the  valves  are 
allowed  to  run  too  long  without  grinding,  these  pits  in  the  valve 
face  will  be  so  deep  that  new  valves  will  be  necessary.  They  will 
also  be  deep  in  the  valve  seat  with  the  result  that  a  correspond- 


GASOLINE   TRACTORS  141 

ingly  longer  time  is  required  to  grind  them  out.  By  grinding  at 
the  proper  intervals,  only  fifteen  to  twenty  minutes  will  be 
required  for  each  valve,  whereas  if  they  are  allowed  to  run  too 
long,  it  may  take  an  hour  or  more  to  get  each  valve  and  its  seat 
into  proper  condition  again.  The  motor  will  also  run  very  much 
better  and  deliver  more  power  if  the  valves  are  kept  in  good  con- 
dition. 

Q.  What  is  the  cause  of  a  valve  leaking  very  badly  at 
times? 

A.  Hard  particles  of  carbon  from  the  cylinder  may  lodge  in 
the  pitted  face  of  the  seat  or  valve  and  prevent  if  from  closing 
tightly.  Even  though  the  valve  be  held  off  its  seat  only  a  few 
thousandths  of  an  inch,  it  cannot  hold  any  compression. 

Q.  What  is  the  cause  of  a  valve  binding  so  that  it  will  not 
operate? 

A.  Worn  valve  guides  will  sometimes  permit  sufficient  side 
play  to  cause  the  valve  stem  to  become  bent.  Lack  of  lubrication 
and  an  accumulation  of  dirt  and  carbon  in  the  valve  guide- will 
cause  the  valve  stem  to  expand  to  a  point  where  it  binds  hard 
and  fast  in  the  guide. 

Q.  What  causes  a  valve  head  to  warp  so  that  the  valve 
must  be  replaced? 

A.  It  may  be  caused  by  overheating  of  the  motor  due  to 
partial  failure  of  the  cooling  system,  such  as  may  be  caused  by  a 
slipping  fan  belt,  trouble  with  the  circulating  pump,  shortage  of 
water  in  the  system,  or  the  clogging  of  some  of  the  pipes  or  the 
radiator.  An  accumulation  of  sediment  or  scale  in  the  jackets  or 
the  radiator  may  have  the  same  effect. 

Q.     Do  valve  springs  ever  need  replacement? 

A.  In  the  course  of  a  season's  use,  the  temper  may  be 
drawn  sufficiently  to  make  the  valve  action  sluggish,  particularly 
in  a  motor  that  runs  very  hot,  but  ordinarily  the  valve  springs  do 
not  often  need  replacement. 

Q.  Is  it  ever  necessary  to  check  the  valve  timing  of  the 
engine? 

A.  It  is  never  necessary  except  in  reassembling  the  engine 
after  it  has  been  taken  down.  Since  the  camshafts  are  made  with 
the  earns  integral,  no  relative  movement  of  the  cams  is  possible 


142  GASOLINE  TRACTORS 

and  it  is  only  necessary  to  time  one  cylinder.  Most  engines  have 
reference  points  by  which  the  valve  timing  may  be  checked  when 
reassembling  the  engine. 

PISTONS 

Q.     What  attention  do  the  pistons  require? 

A.  The  piston  rings  will  wear  to  such  a  degree  that  the 
pistons  no  longer  hold  the  compression  and  there  is  a  substantial 
falling  off  in  the  power. 

Q.     How  often  should  it  be  necessary  to  replace  the  piston  rings? 

A.  This  will  depend  entirely  upon  the  care  that  is  taken  to 
keep  dirt  out  of  the  lubricating  oil  and  to  prevent  its  entrance  to 
the  motor  through  the  carburetor.  If  the  oil  is  handled  carelessly, 
containers  being  allowed  to  stand  uncovered  and  a  film  of  dust 
settling  on  them,  or  if  the  carburetor  is  not  provided  with  an  air 
cleaner,  a  great  deal  of  grit  will  find  its  way  into  the  motor  and 
will  grind  the  piston  rings  down  rapidly  and  also  the  bearings. 

Q.     How  may  the  pistons  be  tested  for  tightness? 

A.  The  valves  being  in  good  condition,  preferably  recently 
ground,  the  test  may  be  made  as  previously  described  for  testing 
the  valves;  or,  with  the  handhole  plates  off  the  crankcase,  have  an 
assistant  turn  the  motor  over  slowly  and  note  whether  there  is  any 
sound  of  air  blowing  down  past  the  pistons  into  the  crankcase. 
Put  a  few  ounces  of  fresh  oil  into  each  cylinder  through  the  spark 
plug  openings,  replace  the  plugs,  and  repeat  the  test.  Loss  of 
compression  may  be  due  entirely  to  poor  lubrication.  Drain  the 
crankcase,  wash  out  with  kerosene,  and  replenish  the  oil  supply; 
and  test  in  the  same  manner. 

Q.  Is  wear  of  the  piston  rings  the  only  cause  for  loss  of 
compression,  aside  from  pitted  valves? 

A.  An  accumulation  of  carbon  under  the  piston  rings  may 
be  holding  the  piston  ring  joints  apart  or  the  latter  may  have  all 
worked  into  line  so  that  the  pressure  is  escaping  through  them. 
If,  with  good  tight  valves,  there  is  still  a  loss  of  compression  after 
putting  fresh  oil  into  the  cylinders,  it  is  an  indication  that  the 
piston  rings  need  attention. 

Q.  Does  the  compression  fail  in  all  the  cylinders  equally,  or 
is  one  of  the  cylinders  likely  to  be  worse  than  the  rest? 


GASOLINE   TRACTORS  143 

A.  The  wear  is  likely  to  be  uneven,  so  that  one  or  two  of 
the  cylinders  will  be  found  very  much  worse  than  the  rest.  Some- 
times only  one  cylinder  will  fail  to  hold  compression.  Test  in  the 
same  manner  as  described  for  the  valves,  pulling  the  crank  up 
very  slowly  to  note  the  resistance  offered  by  each  piston  in  turn 
as  it  comes  up  on  the  compression  stroke.  It  may  be  found  much 
easier  to  move  one  of  the  pistons  than  the  others.  When  this  is 
the  case,  it  will  be  necessary  to  fit  new  rings  on  that  piston. 

Q.     How  are  new  piston  rings  fitted? 

A.  Oversize  piston  rings  are  supplied  for  this  purpose. 
They  are  slightly  larger  (a  few  thousandths  of  an  inch)  than  those 
originally  supplied  with  the  motor  in  order  to  compensate  for  the 
wear  of  the  cylinder.  Take  the  old  rings  off  by  inserting  thin 
strips  of  steel  (old  table-knife  blades  or  discarded  hack  saws  are 
excellent  for  the  purpose)  at  three  or  four  points  around  the  piston 
and  under  the  ring.  Scrape  and  wash  out  all  carbon  and  gummed 
oil  in  the  slots.  Do  not  use  a  file  for  this  purpose.  First  try  the 
new  rings  by  fitting  them  in  the  cylinder,  which  operation  will 
show  how  much  will  have  to  be  taken  off  to  allow  them  to  enter 
the  bore.  They  must  be  small  enough  to  insert  an  inch  or  two 
into  the  cylinder,  since  it  is  turned  somewhat  larger  for  a  short 
distance  at  the  end.  If  the  rings  are  too  large,  take  a  few  cuts 
with  a  fine  file  across  the  faces  of  the  joint,  being  careful  to  keep 
the  surfaces  square  and  parallel.  Very  little  must  be  taken  off 
each  time  and  the  ring  tried  in  the  cylinder  again.  The  job  must 
be  carried  out  with  painstaking  care  as  unless  it  is  properly  done 
the  new  rings  will  be  no  better  than  the  old  ones.  When  they 
have  been  properly  fitted,  use  the  same  strips  to  place  them  on 
the  piston,  care  being  taken  not  to  spring  the  rings  out  of  round 
in  putting  them  on. 

Q.  When  fitting  rings  in  the  cylinder  as  a  preliminary  to 
putting  them  on  the  piston,  should  the  break  come  together  for  a 
good  fit? 

A.  No;  allowance  must  be  made  for  the  lengthwise  expan- 
sion of  the  ring  due  to  the  high  temperature,  and  this  allowance 
must  be  greater  for  the  top  ring  than  for  the  lower  ones  as  it 
becomes  hotter.  Depending  upon  the  diameter  of  the  cylinder, 
it  is  customary  to  allow  yf fa  to  T%fa  inch  between  the  ends  of  the 


144  (iASOLINM    TRACTORS 


topmost  ring  and  re^  to  T^¥¥  inch  for  the  other  two.  Bearing 
shims  are  often  stamped  with  the  thickness  in  thousandths  of  an 
inch  and  may  be  used  as  a  gage.  Unless  this  allowance  is  made, 
the  expansion  of  the  ring  will  cause  it  to  bind  against  the  cylinder 
wall  and  may  cause  scoring. 

Q.     Must  the  piston  ring  be  a  tight  fit  in  the  piston  slot? 

A.  Allowance  for  expansion  must  also  be  made  here.  After 
scraping  the  piston  slots  free  of  carbon  and  washing  them  out 
with  kerosene  so  that  they  are  perfectly  clean,  insert  the  ring  and 
see  that  it  turns  freely  in  the  slot.  A  piece  of  coated  catalog 
paper  lias  a  thickness  of  nroo  to  rcfo^  inch  and  it  should  be  possi- 
ble to  insert  a  piece  of  this  paper  between  the  ring  and  the  slot. 
If  the  rings  are  too  tight  they  will  bind  on  the  piston  and  cause 
damage  as  mentioned  above.  Unless  they  can  be  moved  freely  in 
the  slots,  they  will  have  to  be  made  smaller  by  taking  metal  off 
the  bottom  edge  of  the  ring.  Smear  some  valve  grinding  com- 
pound on  a  flat  metal  plate  or  a  smooth  piece  of  hardwood  plank 
and  rotate  the  ring  in  this  under  pressure  with  the  hand.  Be  sure 
to  wash  off  all  traces  of  the  grinding  compound  before  trying  on 
the  piston  again. 

Q.     Do  the  pistons  themselves  ever  have  to   be  replaced? 

A.  The  same  condition  that  causes  rapid  wear  of  the  piston 
rings,  that  is,  dirt  in  the  lubricating  oil,  will  also  cause  equally 
rapid  wear  of  the  pistons.  When  this  wear  amounts  to  jito"  to 
ylno"  inch,  the  piston  will  rock  on  the  piston  pin  in  the  cylinder 
and  produce  a  distinctive  noise,  known  as  piston  .v/r//>,  which  can- 
not l>e  traced  to  any  other  cause.  At  first,  it  is  likely  to  be  attrib- 
uted to  a  loose  bearing,  and  as  it  increases  it  will  greatly  resemble 
a  bearing  knock.  When  one  piston  reaches  this  stage,  it  is  better 
to  replace  all  of  them  with  oversize  pistons.  The  cylinders  should 
be  examined  carefully  for  scoring  and  tested  to  see  if  they  have 
worn  out  of  round  as  it  may  be  necessary  to  rebore  them  or  to 
replace  the  cylinder  casting  to  make  a  good  job  of  it. 

Q.  Can  the  pistons  be  tested  for  looseness  without  taking 
the  motor  down  when  a  knock  cannot  be  traced  to  any  other 
cause? 

A.  The  amount  of  wear  that  will  cause  considerable  piston 
slapping  is  so  small  that  it  would  b?  difficult  to  detect  it  without 


GASOLINE   TRACTORS  145 

having  the  cylinder  and  piston  on  a  bench  where  the  fit  can  be 
examined  closely.  The  average  driver  would  never  attribute  the 
loud  knocking  caused  by  a  loose  piston  to  the  apparently  slight 
amount  of  play  that  is  revealed  when  the  piston  is  examined. 

Q.  What  causes  besides  dirt  in  the  lubricating  oil  will 
bring  about  rapid  wear  of  the  pistons  or  scoring  of  the  cylinders? 

A.  Other  causes  are  the  use  of  a  poor  grade  of  oil,  using  the 
same  oil  too  long,  or  any  other  condition  that  results  in  inefficient 
lubrication,  such  as  overheating  due  to  partial  failure  of  the  cooling 
system.  Unless  there  is  a  good  oil  film  between  the  piston  and 
the  cylinder,  the  metal  comes  into  actual  contact  and  scoring  fol- 
lows. Too  thin  an  oil  will  be  burned  away  by  the  heat  of  the 
explosion  as  fast  as  the  film  is  formed  on  the  cylinder,  while  too 
heavy  an  oil  may  not  reach  the  upper  end  of  the  cylinder  bore 
owing  to  failure  to  pass  the  piston  rings.  Worn  piston  rings  will 
permit  particles  of  carbon  from  the  combustion  chamber  to  work 
between  the  piston  and  the  cylinder  wall.  Partial  failure  of  the 
lubrication  system,  such  as  the  clogging  of  an  oil  lead  in  a  force- 
feed  system,  the  clogging  of  the  screen  or  of  the  pump  in  a  circu- 
lating system,  or  an  insufficient  supply  of  oil  in  a  splash  system, 
will  result  in  scoring. 

Cylinder  scoring  may  be  due  to  the  piston  ring  binding 
owing  to  failure  to  allow  for  expansion  in  fitting  or  to  the  piston 
sticking  owing  to  an  accumulation  of  carbon  under  it.  The  wrist 
pin  may  become  loose  and  move  endways  so  that  it  scrapes  against 
the  cylinder  wall;  or  in  assembling  the  piston  and  connecting  rod, 
the  wrist  pin  may  be  so  placed  that  it  presses  the  piston  unevenly 
against  one  side  of  the  cylinder.  Carelessness  in  valve  grinding 
that  results  in  some  of  the  compound  getting  into  the  cylinder  will 
cause  serious  scoring  sooner  than  almost  anything  else. 

CARBURETOR 

Q.    What  attention  does  the  carburetor  need? 

A.  It  should  be  drained  at  frequent  intervals  to  remove  the 
accumulation  of  sediment.  Care  should  be  taken  to  prevent  dirt 
from  getting  into  the  fuel,  and  the  latter  should  be  strained  as  it  is 
poured  into  the  tank.  In  making  needle-valve  adjustments,  the 
needle  must  never  be  screwed  down  hard  on  its  .seat,  since  this  is 


146  GASOLINE   TRACTORS 

likely  to  turn  a  shoulder  on  it  so  that  proper  adjustments  cannot 
be  made  with  it. 

Q.  When  the  carburetor  floods,  what  is  the  usual  cause  of 
the  trouble? 

A.  The  usual  cause  is  dirt  lodging  under  the  needle  valve  in 
the  float  chamber.  Where  a  hollow  copper  float  is  used,  it  may 
have  sprung  a  leak,  causing  it  to  skik. 

Q.  How  should  the  carburetor  be  adjusted  to  give  the  maxi= 
mum  power  with  the  most  economical  fuel  consumption? 

A.  Definite  instructions  covering  every  make  of  carburetor 
cannot  be  given,  but  the  same  principles  can  be  applied  to  all. 
With  the  motor  running,  cut  down  the  fuel  supply  gradually  until 
the  motor  begins  to  run  irregularly  or  to  miss.  The  fuel  mixture 
is  thus  made  leaner,  and  in  some  cases  the  motor  will  back  fire 
through  the  carburetor  when  the  mixture  becomes  too  lean. 
When  the  point  of  adjustment  has  been  found  at  which  the  motor 
is  not  getting  sufficient  fuel,  turn  back  slightly  until  just  enough 
fuel  is  being  supplied  to  permit  it  to  idle  regularly.  This  is 
termed  the  low-speed  adjustment  and  some  carburetors  have  no 
other,  that  is,  only  the  fuel  supply  can  be  regulated.  Others  have 
a  high-speed  adjustment  as  well;  this  controls  the  air  supply  and 
takes  the  form  of  an  adjustable  auxiliary  air  valve.  Speed  the 
motor  up  and  release  the  tension  of  the  auxiliary  air  valve  spring 
until  the  point  is  reached  where  too  much  air  is  being  admitted 
and  the  mixture  again  becomes  too  lean.  Then  turn  back  slowly 
until  as  much  air  is  being  admitted  as  is  possible  without  causing 
irregular  operation. 

Q.  Does  the  working  of  any  other  part  of  the  motor  influ- 
ence  the  carburetor  adjustment? 

A.  Unless  all  other  parts  of  the  motor  are  in  good  working 
condition,  it  will  be  found  impossible  to  make  a  satisfactory  car- 
buretor adjustment.  Valves  in  need  of  grinding,  excessive  clear- 
ance between  valve  tappets  and  stems  or  rocker  arms,  worn  piston 
rings  or  pistons,  and  worn  valve  guides  will  all  influence  the  adjust- 
ment of  the  carburetor.  Air  drawn  in  through  worn  valve  guides, 
a  leaky  intake  manifold,  or  a  leak  at  the  throttle  valve  of,  the 
carburetor  will  weaken  the  mixture  and  make  it  too  lean,  so  that 
the  motor  loses  power  and  overheats.  With  the  motor  running, 


GASOLINE   TRACTORS  147 

take  a  squirt  can  and  put  some  gasoline  on  the  intake  manifold 
gaskets  and  around  the  valve  stems  and  note  whether  it  is  drawn 
in  or  not.  New  gaskets  will  remedy  trouble  of  this  nature  at  the 
manifold.  Whenever  the  manifold  has  to  be  taken  down,  it  is 
always  better  to  replace  the  gaskets,  since  it  is  difficult  to  make 
used  gaskets  tight. 

Q.  The  float  valve  and  needle  adjustment  being  in  good 
condition,  what  is  the  cause  of  the  trouble  when  a  regular  flow 
of  fuel  cannot  be  obtained  at  the  nozzle  in  the  mixing  chamber? 

A.  The  supply  line  may  be  partially  clogged  or  tjie  vent  hole 
in  the  top  of  the  carburetor  may  Be  stopped  up.  This  is  a  small 
opening  designed  to  admit  air  in  order  that  there  may  be  atmos- 
pheric pressure  on  the  fuel  in  the  float  chamber.  If  this  clogs  up, 
a  partial  vacuum  is  formed.  In  a  gravity  system  the  air  vent  on 
the  tank  may  have  become  stopped  up  and  the  fuel  will  not  flow 
to  the  carburetor  owing  to  the  lack  of  atmospheric  pressure  on  top 
of  the  supply.  In  a  pressure  or  a  vacuum  tank  supply  system  the 
trouble  may  be  with  the  pump,  or  with  loose  joints,  or  with  the 
tank  itself. 

Q.  When  difficulty  is  experienced  in  making  a  satisfactory 
low=speed  adjustment,  what  is  likely  to  be  the  cause? 

A.  The  needle  valve  may  have  been  forced  down  on  its  seat 
so  that  a  burr  or  ring  has  been  formed  on  the  needle.  The  latter 
should  be  taken  out  and  repointed. 

Q.  Is  an  air  cleaner  indispensable  in  connection  with  a 
tractor  carburetor? 

A.  It  will  save  its  cost  and  the  time  required  to  attend  to  it 
many  times  over.  Without  it,  pistons,  rings,  and  bearings  will 
grind  out  very  rapidly,  and  trouble  will  be  experienced  with 
accumulations  of  carbon,  more  than  half  of  which  will  be  nothing 
more  nor  less  than  dirt  drawn  in  through  the  carburetor. 

Q.     What  attention  does  the  air  cleaner  require? 

A.  Frequent  cleaning  is  the  only  attention  needed.  When 
the  cleaner  is  of  the  dry-air  type,  the  engine  should  always  be 
shut  down  before  emptying  it.  If  it  is  a  washer  type,  see  that  it 
is  constantly  supplied  with  plenty  of  water.  Clean  out  either 
type  twice  a  day  or  oftener,  if  necessary,  rather  than  wait  until  it 
is  full.  Analyses  of  carbon  accumulations  taken  from  automobile 


148  GASOLINE  TRACTORS 

cylinders  have  shown  them  to  consist  of  65  per  cent,  or  more,  of 
road  dirt. 

Q.     How  can  an  over=rich  mixture  be  detected? 

A.  Note  the  color  of  the  exhaust  from  the  muffler.  The 
presence  of  black  smoke  indicates  that  too  much  fuel  is  being  fed; 
blue  smoke,  too  much  lubricating  oil;  and.  grayish-white  smoke, 
poor  combustion  of  kerosene  usually  due  to  an  excess  of  water. 
An  over-rich  mixture,  particularly  when  kerosene  is  being  used,  will 
cut  the  lubricating  oil  from  the  cylinder  walls  and  cause  scoring 
unless  remedied. 

Q.    What  is  the  object  of  feeding  water  with  the  fuel? 

A.  To  assist  in  keeping  the  temperature  of  the  engine  down 
to  the  proper  point  for  satisfactory  working.  The  steam  generated 
rapidly  absorbs  a  great  deal  of  the  heat  and  has  the  further 
advantage  of  preventing  the  formation  of  carbon  in  the  cylinders. 
It  also  causes  better  combustion,  particularly  in  the  case  of  kerosene. 

Q.  Should  water  be  fed  with  the  fuel  regardless  of  the 
grade  of  oil  employed? 

A.  Little  or  no  water  is  necessary  when  using  gasoline,  but 
the  majority  of  motors  will  not  operate  satisfactorily  on  kerosene 
without  it. 

Q.  Is  there  any  danger  of  feeding  too  much  water,  par- 
ticularly when  the  motor  is  running  very  hot  and  appears  to 
need  it? 

A.  Excess  water  fed  with  the  fuel  is  liable  to  lower  the 
temperature  to  the  point  at  which  kerosene  recoridenses  to  a 
liquid;  in  such  a  case  considerable  of  it  works  its  way  past  the 
pistons  and  down  into  the  crankcase.  This  destroys  the  film  of 
lubricant  on  the  cylinder  walls  and  is  liable  to  cause  damage,  not 
alone  to  the  cylinders  themselves  but  likewise  to  the  bearings; 
thinning  the  oil  in  the  crankcase  destroys  its  lubricating  qualities. 
If  the  motor  appears  to  be  getting  too  hot,  the  trouble  should  be 
remedied  by  locating  the  fault  in  the  cooling  or  the  lubricating 
system  and  not  by  attempting  to  overcome  it  by  increasing  the 
amount  of  water  fed. 

Q.    What  indication  is  there  of  excessive  water  in  the  fuel? 

A.  A  grayish  white  smoke  will  appear  at  the  exhaust  indi- 
cating that  the  kerosene  is  not  being  completely  burned  in  the 


GASOLINE  TRACTORS  149 

cylinders.  Cut  down  the  water  supply  very  gradually  until  the 
smoke  disappears,  the  motor  being  kept  running  at  a  good  speed, 
since  if  run  too  slowly  on  kerosene  the  combustion  of  the  latter 
will  not  be  complete  owing  to  the  drop  in  temperature. 

Q.  Are  all  tractor  motors  provided  with  hand=controlled 
apparatus  for  feeding  water? 

A.  No;  some  carburetors  are  designed  to  feed  water  auto- 
matically as  it  is  needed,  while  in  others- the  use  of  a  wet  air 
cleaner  is  depended  upon  to  supply  the  proper  amount  of  water 
required. 

Q.  Where  hand  control  is  provided,  should  the  water  be 
fed  as  long  as  the  engine  is  running? 

A.  It  is  better  to  shut  it  off  five  minutes  or  so  before  the 
motor  is  to  be  stopped,  and  the  fuel  should  be  switched  from  kero- 
sene to  gasoline  at  the  same  time,  as  this  will  leave  the  motor  in 
better  condition  and  facilitate  restarting. 

Q.  What  precautions  should  be  taken  with  the  water  sup= 
plied  for  this  purpose? 

A.  Clean  rain  water  should  be  used,  and  it  is  well  to  strain 
it  through  two  or  three  thicknesses  of  cloth  to  prevent  the  entrance 
of  any  dirt. 

COOLING   SYSTEM 

Q.  When  the  engine  overheats  despite  the  fact  that  the 
cooling  system  is  working  properly,  what  is  the  cause  of  the 
trouble? 

A.  It  may  be  due  either  to  an  over-rich  or  an  over-lean 
mixture.  In  either  case  combustion  is  slow  instead  of  taking  the 
form  of  the  explosion  required  to  produce  the  maximum  power. 
The  mixture  continues  to  burn  throughout  the  stroke  and  in  the 
exhaust  passages  and  muffler.  Flame  issuing  from  the  exhaust  is 
an  indication  of  this  condition.  The  ignition  may  be  retarded  too 
far  and  bring  about  the  same  condition. 

Q.  What  are  some  of  the  causes  of  failure  of  the  cooling 
system? 

A.  Among  the  causes  are  the  following:  insufficient  water 
supply;  fan  belt  slipping;  pump  running  too  slow  when  driven  by  a 
belt;  insufficient  lubrication;  leaks  in  radiator  or  at  pump  packing 
permitting  water  to  escape  or  air  to  enter;  and  clogging  of  radia- 


150  GASOLINE   TRACTORS 

tor,  circulating  pipes,  or  water  jackets  with  an  accumulation  of 
sediment.  The  cooling  system  should  be  drained  at  frequent 
intervals  and  flushed  out  with  clean  water.  An  accumulation  of 
carbon  in  the  cylinders  will  also  cause  the  engine  to  overheat  and 
if  allowed  to  become  very  bad,  will  cause  preignition,  which 
imposes  very  heavy  stresses  on  all  moving  parts  of  the  engine. 

Q.  When  hard  water  has  to  be  used  in  the  cooling  system 
and  scale  forms,  how  can  this  be  removed? 

A.  A  strong  soda  solution  made  by  adding  several  pounds  of 
common  washing  soda  to  enough  boiling  water  to  fill  the  system 
should  be  used  for  a  day  or  so  in  place  of  ordinary  water.  The 
system  should  then  be  drained  and  flushed  out.  The  use  of  rain 
water  will  prevent  the  formation  of  scale.  Particles  of  iron  rust 
in  the  water  when  the  system  is  flushed  should  not  be  confused 
with  scale;  these  will  always  be  found,  even  if  the  system  is 
drained  every  day. 

Q.     Do  the  flexible=hose  connections  ever  cause  any  trouble? 

A.  The  inner  plies  of  the  hose  sometimes  become  detached 
owing  to  the  high  temperature  of  the  cooling  water  and  either 
partially  or  wholly  clog  the  passage.  The  passage  is  liable  to 
become  wholly  clogged  with  the  pump  type  of  circulation  owing  to 
the  much  smaller  diameter  of  the  hose  used.  To  guard  against 
trouble  of  this  nature,  use  nothing  but  the  hose  connections  sup- 
plied by  the  manufacturers  as  replacements  since  this  hose  is 
specially  made  to  withstand  hot  water.  Ordinary  hose  will  dis- 
integrate rapidly  when  employed  for  this  purpose  and  should 
never  be  so  used  except  to  tide  over  an  emergency,  being  replaced 
with  a  new  connection  as  soon  as  possible. 

Q.  Is  partial  or  total  failure  of  the  cooling  system  the  only 
cause  of  overheating? 

A.  No;  there  are  numerous  other  causes  of  overheating. 
The  motor  may  be  run  with  the  ignition  retarded;  the  lubrication 
may  not  be  efficient;  or  carbon  may  have  accumulated  in  the 
combustion  chambers,  as  pointed  out  in  a  previous  answer. 

Q.  How  can  carbon  be  prevented  from  accumulating  in  the  motor? 

A.  After  the  motor  has  been  shut  down  for  the  day  and  is 
very  hot,  take  out  the  spark  plugs,  turn  the  motor  over  by  hand 
until  all  the  pistons  are  at  approximately  the  same  height,  and 


GASOLINE  TRACTORS  151 

pour  into  each  cylinder  about  an  ounce  of  kerosene,  letting  it 
stand  this  way  over  night.  Do  not  use  more  than  this  amount  of 
kerosene  (a  tablespoon  will  hold  about  an  ounce)  on  the  theory 
that  if  a  little  does  good,  more  will  do  better,  since  more  kerosene 
will  cut  the  lubricating  film  off  the  cylinder  walls  and  thin  the  oil 
in  the  crankcase. 

Q.     How  can  the  fan  belt  be  kept  in'good  condition? 

A.  Make  adjustments  only  when  the  motor  is  hot  and  do 
not  put  any  more  tension  on  the  belt  than  is  necessary  to  prevent 
slipping.  A  belt  that  is  set  up  too  tightly  will  wear  very  quickly 
besides  imposing  undue  stresses  on  the  pulley  bearings.  Keep  the 
leather  soft  by  applying  neatsfoot  oil  from  time  to  time. 

Q.  How  often  should  the  radiator  and  cooling  system  be 
drained? 

A.  Two  or  three  times  a  season  are  sufficient  in  summer  if 
clean  rain  water  is  being  used  and  it  is  strained  before  being  put 
into  the  radiator.  In  winter  it  will  be  found  better  practice  to 
drain  the  entire  system  every  night  rather  than  to  depend  upon 
an  anti-freezing  solution,  since  the  latter  lowers  the  boiling  point 
of  the  water  to  such  an  extent  that  it  is  likely  to  boil  away.  In 
any  case,  if  alcohol  is  used  in  the  anti-freezing  solution,  it  is 
likely  to  boil  out  of  the  water,  so  that  the  latter  cannot  be  left  in 
over  night  with  safety.  Some  tractors  are  cooled  by  oil,  and  in 
cold  weather  it  is  necessary  to  thin  this  oil  with  kerosene  before  it 
will  circulate  freely. 

Q.  When  it  is  discovered  that  a  considerable  quantity  of 
the  water  has  boiled  away  and  the  motor  is  very  hot,  is  it  good 
practice  to  fill  up  with  cold  water  immediately? 

A.  This  should  not  be  done,  particularly  in  winter,  as  the 
fresh  supply  is  likely  to  be  very  cold  and  the  sudden  contraction 
would  impose  severe  stresses  on  the  radiator  joints,  starting  leaks. 

Q.  What  attention  does  the  pump  of  a  circulating  system 
require? 

A.  See  that  the  glands  are  kept  tight.  The  appearance  of  a 
drop  of  water  at  the  gland  indicates  the  beginning  of  a  slow  leak. 
Give  the  gland  nut  a  partial  turn  to  tighten  it;  if  water  still 
appears,  it  will  be  necessary  to  repack  the  stuffing  box.  Use  oil- 
soaked  cotton  wick  or  graphite  packing. 


152  GASOLINE  TRACTORS 

HORSEPOWER   RATINGS 

Q.  Why  are  tractors  rated  as  10-20,  16-30,  etc.,  always 
giving  two  horsepower  ratings? 

A.  Tractors  are  designed  to  be  used  for  belt  as  well  as  for 
field  work.  In  doing  the  latter,  the  tractor  must  use  a  substantial 
percentage  of  its  power  to  move  itself.  The  lower  rating  accord- 
ingly expresses  the  amount  of  power  available  for  plowing.  When 
standing,  as  in  performing  belt  work,  the  only  losses  are  caused  by 
whatever  transmission  gearing  is  interposed  between  the  engine 
and  the  belt  pulley,  so  that  almost  the  entire  output  of  the  power 
plant  is  available  for  driving  other  machinery. 

Q.  What  constitutes  an  overload,  and  why  do  all  manu= 
facturers  warn  the  tractor  user  so  strongly  against  subjecting 
the  machine  to  overloads? 

A.  Considerable  confusion  exists  as  to  the  meaning  of  the 
term  horsepower.  For  a  few  minutes,  as  in  pulling  out  of  a  hole, 
a  heavy  draft  horse  is  capable  of  exerting  600  to  800  pounds  draw- 
bar pull,  which  is  the  equivalent  of  more  than  1  hp.,  but  the 
same  horse  cannot  exert  much  more  than  an  average  of  100  pounds 
drawbar  pull  at  a  speed  of  three  miles  an  hour  in  hauling  a  load 
all  day.  The  fact  that  a  tractor  having  a  field  rating  of  16  hp. 
may  be  pulled  out  of  a  bad  place  by  three  heavy  horses  does  not 
indicate  that  the  team  is  capable  of  doing  as  much  work  as  the 
machine.  The  animals  can  only  exert  this  much  power  for  a  very 
short  period.  The  tractor  will  generate  an  amount  of  power  at 
the  drawbar  equivalent  to  fourteen  or  fifteen  horses  at  the  usual 
plowing  speed  and  will  keep  it  up  all  day.  A  load  such  as 
twelve  horses  could  haul  all  day  would  represent  the  practical 
working  maximum  for  such  a  machine.  A  heavier  load  than  this, 
apart  from  emergencies  which  call  for  all  the  power  the  machine 
can  produce  for  only  a  very  short  period,  would  represent  an  over- 
load for  that  tractor.  In  other  words,  the  tractor  should  not  be 
steadily  subjected  to  a  load  amounting  to  more  than  75  per  cent 
of  its  capacity.  Manufacturers  warn  tractor  owners  against  over- 
loading their  machines  because  tractors  will  wear  out  very  quickly 
under  the  excessive  strain  and  will  not  give  satisfactory  service 
during  the  machine's  greatly  reduced  useful  life.  Regardless  of 
the  plow  rating  of  the  tractor,  as  for  instance,  three-plow  or  four- 


GASOLINE  TRACTORS  153 

plow,  the  number  of  plows  used  should  depend  upon  the  nature 
of  the  soil.  When  the  latter  is  very  heavy,  or  the  plowing  has  to 
be  done  on  an  up  grade,  fewer  plows  should  be  used.  More  and 
better  work  will  be  done  by  not  subjecting  the  tractor  to  any 
greater  load  than  it  can  pull  without  exerting  more  than  75  per 
cent  of  its  power. 

ENGINE  TROUBLES 
FAILURE  TO  START 

Q.  What  are  some  of  the  commoner  causes  of  failure  to 
start? 

A.  Over  95  per  cent  of  all  failures  to  start  are  due  to  either 
lack  of  fuel  or  lack  of  the  spark  to  ignite  it.  Part  of  the  remain- 
ing 5  per  cent  are  due  to  the  failure  of  the  two  to  come  together 
at  the  right  time,  while  the  rest  may  be  put  down  to  faults  hav- 
ing no  connection  with  either  the  carburetor  or  the  magneto. 

Q.  Does  lack  of  fuel  in  this  connection  mean  an  empty 
tank  and  nothing  more? 

A.  While  a  great  deal  of  energy  has  been  expended  to  no 
good  purpose  in  trying  to  start  an  engine  that  was  connected  to 
an  empty  gasoline  tank,  lack  of  fuel  implies  a  great  deal  more 
than  that.  It  does  not  do  much  good  to  have  a  full  tank  unless 
the  fuel  is  actually  getting  into  the  cylinders  every  time  the 
engine  turns  over.  There  may  be  a  stoppage  between  the  tank 
and  the  carburetor  or  between  the  latter  and  the  cylinders.  A 
plugged  air  vent  either  at  the  tank  or  at  the  carburetor  will  pre- 
vent the  liquid  fuel  from  reaching  the  carburetor  nozzle.  A 
stopped-up  carburetor  nozzle  will  not  vaporize  any  fuel,  while  a 
broken  throttle  connection  which  leaves  the  throttle  closed  will 
not  permit  any  spray  from  an  open  nozzle  to  reach  the  motor,  or 
at  least  not  enough  to  render  starting  easy.  Air  leaks  at  the 
carburetor,  the  manifold,  or  the  valve  stems  will  weaken  the 
mixture  considerably. 

Q.  Is  it  not  as  hard  to  start  with  too  much  fuel  as  with 
too  little? 

A.  Flooding  the  cylinders  makes  starting  very  difficult,  and 
when  this  has  occurred,  the  only  remedy  is  to  shut  off  the  supply 
entirely  and  crank  the  motor  for  a  few  minutes  to  clean  out  the 


154  GASOLINE  TRACTORS 

cylinders.  Priming  too  freely  is  a  bad  practice,  since  the  liquid 
gasoline  cuts  the  lubricating  oil  from  the  cylinder  walls  and 
destroys  the  compression  to  such  an  extent  that  in  an  old  engine 
it  is  next  to  impossible  to  start  even  though  the  fuel  and  the 
spark  come  together  in  the  right  place  at  the  right  time.  This  is 
one  of  the  unspecified  causes  responsible  for  part  of  the  5  per 
cent  of  the  failures  to  start  mentioned  previously.  There  will  be 
a  weak  explosion  every  time  a  cylinder  should  fire,  but  not 
enough  power  will  be  produced  to  cause  the  engine  to  take  up  its 
cycle  and  run. 

Q.  When  the  cylinders  have  been  flooded  by  over=priming 
with  gasoline,  what  should  be  done? 

A.  Close  the  throttle  and  open  the  air  valve  or  choker,  so 
that  no  gasoline  is  drawn  through  the  carburetor.  Take  out  the 
spark  plugs  and  put  2  or  3  ounces  of  heavy  cylinder  oil  into  each 
cylinder.  Replace  the  plugs  and  turn  the  motor  over  for  two  or 
three  minutes  with  the  ignition  off. 

Q.  Has  the  position  of  the  throttle  lever  any  effect  on  the 
fuel  supply  at  starting? 

A.  Some  engines  can  only  be  started  readily  with  the  throttle 
at  a  certain  position,  usually  not  more  than  one-third  open  and 
sometimes  considerably  less.  On  a  cold  morning  opening  the 
throttle  too  far  is  liable  to  allow  too  much  gasoline  in  liquid  form  to 
find  its  way  into  the  cylinders,  so  that  the  effect  is  the  same  as 
that  of  over-priming  or  flooding. 

Q.     How  should  an  engine  be  primed? 

A.  Gasoline  should  be  carried  in  a  squirt  can  for  this  pur- 
pose and  not  more  than  a  teaspoonful  should  be  squirted  into  each 
cylinder  through  the  pet  cocks.  If  the  engine  does  not  start  after 
priming  two  or  three  times,  look  for  some  other  cause  of  fuel  or 
ignition  failure.  If  the  engine  starts  and  only  turns  over  a  few 
times  and  then  stops,  the  cause  is  likely  to  be  lack  of  fuel  as 
indicated  by  the  fact  that  it  ran  on  what  was  injected  into  the 
cylinders.  In  priming  the  float  in  the  carburetor  is  also  depressed 
by  means  of  a  button  or  lever  provided  for  the  purpose.  This 
floods  the  carburetor  and  causes  the  gasoline  to  overflow  through 
the  nozzle  into  the  mixing  chamber.  The  moment  any  gasoline 
leaks  out  of  the  carburetor,  the  float  should  be  released,  since 


GASOLINE  TRACTORS  155 

otherwise  the  cylinders  will  be  flooded.  Never  prime  the  car- 
buretor just  as  the  engine  is  starting,  as  this  will  produce  an 
over-rich  mixture  and  probably  cause  a  pop  back  which  may  ignite 
the  gasoline  in  the  carburetor. 

Q.     Is  water  in  the  gasoline  a  frequent  cause  of  failure  to  start? 

A.  It  may  not  be  a  very  frequent  cause,  but  the  occurrence 
of  any  water  in  the  gasoline  will  make  it  difficult  to  start  the 
motor.  Being  heavier  than  gasoline  the  water  sinks  to  the  bot- 
tom of  the  tank  and  there  may  be  enough  of  it  to  partly  fill  the 
carburetor.  The  remedy  is  to  drain  the  carburetor,  taking  out 
a  half-pint  or  so. 

Q.  What  effect  does  the  use  of  kerosene  as  fuel  have  on 
the  starting  of  the  motor? 

A.  It  has  no  effect,  if  the  matter  is  properly  handled.  At 
least  five  minutes  before  the  engine  is  to  be  stopped  the  kerosene 
should  always  be  shut  off  and  the  engine  allowed  to  run  on  gaso- 
line so  that  all  traces  of  kerosene  will  be  cleaned  out  of  the 
cylinders  and  the  manifold.  If  this  has  not  been  done,  it  will 
take  considerable  cranking  to  start  the  engine,  and  it  may  also  be 
necessary  to  inject  2  or  3  ounces  of  fresh  oil  into  each  cylinder  to 
renew  the  compression  seal  since  the  kerosene  condenses  in  the 
cylinders  as  soon  as  they  get  cold  and  then  runs  down  past  the 
pistons  into  the  crankcase. 

Q.  Will  an  adjustment  of  the  mixture  make  starting  any 
easier? 

A.  The  actual  adjustment  of  the  carburetor  itself  should 
never  be  disturbed  for  starting  purposes,  as,  if  this  is  done, 
either  the  carburetor  will  seldom  be  properly  adjusted  for  efficient 
running  or  a  great  deal  of  time  will  be  spent  unnecessarily  in 
making  adjustments.  Moreover  the  carburetor  parts  will  soon 
wear  badly  and  make  efficient  adjustment  impossible.  Most  car- 
buretors are  provided  with  a  choker  which,  when  closed,  causes  all 
the  air  to  be  drawn  past  the  nozzle,  thus  increasing  the  suction 
and  giving  a  rich  mixture.  This  should  be  closed  for  starting  and 
opened  the  moment  the  motor  gets  under  way.  Ordinarily  the 
running  mixture  is  too  lean  to  make  starting  easy. 

Q.  What  are  the  commoner  causes  of  failure  to  start 
through  ignition  trouble? 


156  GASOLINE  TRACTORS 

A.  Among  the  causes  are  the  following:  a  ground  or  short- 
circuit  in  the  wiring;  points  of  plugs  burned  too  far  apart;  moisture 
on  the  distributor  of  the  magneto;  failure  of  the  contact  points  in 
the  breaker  box  of  the  magneto  to  separate  when  the  cam  strikes 
the  hinged  lever;  impulse  starter  of  magneto  stuck  or  spring 
broken;  putting  plug  cables  on  wrong  plugs  when  a  change  has 
been  made  just  before  attempting  to  start;  badly  sooted  plugs; 
spark  lever  advanced  too  far;  and  loose  connections,  particularly 
where  a  separate  coil  is  used  with  the  magneto. 

Q.  What  simple  test  can  be  made  to  determine  whether 
the  spark  is  occurring  in  each  cylinder  at  the  proper  time? 

A.  Take  out  the  plugs,  leaving  the  cables  attached  to  them, 
and  lay  the  plugs  on  the  cylinder  head.  Then  turn  the  motor 
over  slowly  and  note  whether  or  not  the  sparks  occur  at  the 
plugs  in  the  proper  sequence.  Note  whether  there  is  a  strong 
blast  of  air  from  one  of  the  spark  plug  holes  each  time  the  motor 
is  turned  over;  if  not,  pour  an  ounce  or  two  of  fresh  oil  into  each 
cylinder.  The  failure  to  start  may  be  due  to  lack  of  compression. 

Q.  If,  when  the  spark  plugs  are  thus  placed,  no  spark 
occurs  at  them,  where  should  the  trouble  be  sought? 

A.  Take  off  the  cover  of  the  contact  breaker  of  the  magneto; 
have  an  assistant  turn  the  motor  over  slowly,  and  note  whether 
the  points  of  the  contact  breaker  separate  twice  per  revolution 
(four-cylinder  motor).  If  they  do  separate,  note  whether  the 
faces  of  the  contact  points  are  clean  and  square.  If  they  are 
blackened  or  pitted,  clean  and  true  them  up  with  a  very  fine  file 
or  a  strip  of  fine  sandpaper,  and  then  so  adjust  them  that  they 
come  together  firmly  when  the  cam  is  horizontal  and  do  not 
separate  more  than  -£%  inch  when  the  cam  is  vertical.  By  giving 
the  motor  a  sharp  turn  beyond  a  compression  point  a  spark  will 
be  noted  between  the  points;  or  the  impulse  starter  may  be  used 
and  the  result  noted. 

Q.  Assuming  that  a  spark  takes  place  between  the  contact 
points  of  the  magneto,  but  none  occurs  at  any  of  the  spark  plugs, 
where  should  the  trouble  be  sought? 

A.  Open  up  the  distributor  of  the  magneto  and  wipe  it  free 
of  any  moisture  or  dirt  that  may  have  accumulated  on  it.  Turn 
the  motor  over  and  note  whether  the  distributor  brush  revolves  as 


GASOLINE  TRACTORS  157 

it  should.  Adjust  all  the  spark  plug  gaps  to  not  more  than  -gV 
inch;  see  that  the  plugs  are  properly  cleaned  and  that  they  are 
lying  on  their  sides  on  the  cylinder  heads,  so  that  only  their' 
bodies  come  in  contact  with  the  metal.  If  they  are  so  placed 
that  the  central  electrodes  are  touching,  the  current  will  pass 
through  them  without  causing  a  spark,  since  there  are  then  no 
gaps  for  it  to  jump.  In  case  none  of  these  tests  produces  a 
spark  at  the  plugs,  there  is  more  than  likely  to  be  some  internal 
trouble  with  the  magneto,  though  this  is  of  comparatively  rare 
occurrence. 

Q.  When  the  impulse  starter  fails  to  operate,  what  is  likely 
to  be  the  cause  of  the  trouble? 

A.  Either  the  mechanism  has  become  gummed  up  with  oil 
and  dirt  or  the  spring  has  broken.  Cleaning  out  the  impulse  starter 
with  gasoline  and  re-oiling  will  remove  the  former  cause. 

Q.  When  the  engine  fails  to  start  after  having  been  primed 
once  or  twice  and  cranked  several  times,  in  what  order  should 
the  cause  of  the  trouble  be  sought? 

A.  This  will  depend  largely  upon  weather  conditions.  In 
very  cold  weather  it  is  quite  likely  that  nothing  but  the  low  tem- 
perature is  the  cause  of  difficulty  in  starting.  Results  will  usually 
follow  continued  cranking,  as  this  warms  the  engine  up  somewhat 
and  makes  it  turn  over  easier,  with  the  result  that  the  first  weak 
explosions  may  cause  it  to  take  up  its  cycle.  In  warm  weather, 
if  a  start  does  not  follow  several  attempts  at  cranking,  test  the 
ignition  first  and  then  the  fuel  supply,  applying  the  different  tests 
already  outlined  and  in  about  the  order  given. 

Q.  Are  there  any  other  points  in  the  ignition  system  that 
are  likely  to  be  responsible  for  failure  to  start? 

A.  If,  when  turning  over,  the  motor  produces  a  spark  at  the 
contact  breaker  but  none  at  the  plugs,  investigate  the  magneto 
switch.  It  may  have  become  broken  or  its  connections  may  be 
faulty.  See  that  it  is  in  the  right  position,  sin6e  many  tractor 
motors  can  only  be  stopped  by  short-circuiting  the  magneto  by  means 
of  the  switch.  In  case  the  switch  is  in  the  S  TOP  position,  no  spark 
will  occur  at  the  plugs.  On  some  tractors  the  spark-advance  lever 
takes  the  place  of  the  switch;  by  fully  retarding  it  the  magneto  is 
short-circuited,  and  the  motor  cannot  be  started. 


158  GASOLINE  TRACTORS 

Q.  Do  the  magnets  of  the  magneto  lose  so  much  of  their 
strength  that  no  current  is  produced? 

A.  In  time,  the  heat  and  vibration  are  liable  to  weaken  the 
magneto,  but  this  is  far  from  being  a  common  source  of  trouble. 
If,  after  making  the  tests  mentioned,  no  spark  is  produced,  take 
off  the  distributor  plate  of  the  magneto  and  rest  a  screwdriver 
blade  on  the  gear  casing  so  that  its  end  comes  within  J  inch  of 
the  collector  ring.  Turn  the  motor  over,  and  note  whether  a 
spark  jumps  this  gap.  A  J-inch  spark  at  this  point  will  indicate 
that  there  is  no  falling  off  in  the  power  of  the  magneto.  If  a 
spark  cannot  be  produced  in  this  way,  there  is  something  wrong 
with  the  magneto  itself,  and  it  should  be  sent  to  the  manufac- 
turer for  repairs.  Ordinarily  remagnetization  is  only  necessary  if 
the  magneto  has  been  taken  apart  and  the  magnets  allowed  to 
stand  without  a  "keeper,"  or  piece  of  soft  iron  across  their  ends, 
or  if  they  have  been  removed  from  the  magneto  and  reassembled 
in  the  wrong  way. 

Q.  When  the  contact  points  have  become  so  badly  pitted 
and  burned  away  that  they  cannot  be  properly  adjusted  after 
cleaning  and  trueing  up,  what  should  be  done? 

A.  One  or  both  of  the  contacts  should  be  replaced  and 
adjusted  properly.  The  magneto  manufacturer  usually  supplies  a 
special  wrench  for  this  purpose,  one  end  of  it  serving  as  a  gage 
for  the  proper  gap  between  them.  The  lock  nut  of  the  movable 
point  should  always  be  screwed  down  firmly  after  the  adjustment 
has  been  made  or  it  will  back  off  owing  to  the  vibration. 

Q.  Are  there  any  connections  on  the  magneto  which  are 
likely  to  become  short=circuited  or  grounded? 

A.  When  the  wire  is  brought  out  through  the  side  of  the 
magneto,  the  insulation  may  become  so  worn  that  the  metal 
touches  the  side  of  the  opening,  causing  a  short-circuit.  In  the 
inductor  types  of  magneto,  such  as  the  Remy  and  K-W,  this  is 
most  likely  to  occur  at  the  grounding  screw  where  the  wire  is 
fastened  to  the  side  of  the  magneto.  In  shuttle-wound  types, 
such  as  the  Eisemann,  Kingston,  and  Bosch,  the  break  may  be 
at  the  point  where  the  wire  is  fastened  to  the  armature  or  where 
it  is  fastened  to  the  collector  ring. 

Q.    Can  the  contact  breaker  become  short-circuited? 


GASOLINE  TRACTORS  159 

A.  Metallic  dust  or  filings  will  be  liable  to  cause  this;  the 
remedy  is  to  clean  out  the  inside  of  the  box  with  gasoline.  When- 
ever an  adjustment  is  made,  the  contact  points  must  always  be 
redressed  so  as  to  come  together  squarely.  For  this  purpose  use 
only  the  small  file  supplied  by  the  manufacturer,  and  take  off  just 
as  little  of  the  platinum  as  possible,  since  it  is  worth  consider- 
ably more  than  gold. 

Q.  How  can  the  contact=breaker  box  be  tested  for  a  short- 
circuit? 

A.  Remove  it  from  the  magneto,  place  a  piece  of  paper 
between  the  points,  and  then  hold  the  box  within  J  inch  of  the 
shaft  while  the  magneto  is  turned  over  with  the  other  hand.  No 
spark  should  occur;  if  it  does,  it  indicates  that  the  insulation  of 
the  adjustable  contact  point  is  poor  and  should  be  replaced. 
The  test  should  then  be  repeated  with  the  paper  removed  so  that 
the  points  are  in  contact;  a  spark  should  then  occur  when  the 
armature  is  turned  over,  the  breaker  box  being  held  within  J 
inch  or  less. 

Q.  Does  oil  getting  on  the  parts  injure  the  magneto  in  any 
way? 

A.  If  allowed  to  get  between  the  contact  points  in  the 
breaker  box,  it  will  insulate  them.  On  the  shuttle-wound  types  of 
magneto  there  is  a  collector  ring  and  brush,  and  allowing  any  oil 
to  get  on  them  will  prevent  the  operation  of  the  magneto  alto- 
gether. Oil  usually  carries  more  or  less  dirt  with  it,  and  if 
allowed  to  get  on  the  distributor,  it  is  liable  to  cause  leakage  of  the 
high-tension  current,  so  that  no  spark  occurs  at  the  plugs. 

Q.  How  often  should  the  contact  points  of  the  magneto 
need  attention? 

A.  This  will  depend  more  or  less  on  the  particular  type  of 
magneto  and  the  engine,  but  they  should  be  inspected  at  least 
once  every  thirty  days  while  the  tractor  is  in  service  steadily  and 
trued  up  with  the  sandpaper  or  special  file  whenever  the  slightest 
irregularity  of  their  surfaces  is  evident.  Taking  off  a  little  at  fre- 
quent intervals  will  keep  the  points  in  much  better  condition  and 
will  save  the  costly  platinum,  since  once  the  points  start  to  pit 
this  process  proceeds  very  rapidly.  Emery  should  never  be  used 
on  the  points. 


160  GASOLINE  TRACTORS 

Q.     Is  excess  oil  in  the  motor  ever  a  cause  of  failure  to  start? 

A.  When  there  is  so  much  oil  in  the  motor  that  considerable 
of  it  finds  its  way  into  the  combustion  chambers,  it  will  collect  on 
the  spark  plug  points  and  insulate  them,  if  unburned,  or  short- 
circuit  them,  if  carbonized.  The  fact  that  the  motor  apparently 
ran  satisfactorily  just  before  being  shut  down  the  last  time  is  not 
conclusive  evidence  that  the  spark  plugs  are  in  good  condition. 
The  magneto  generates  a  high  voltage  when  running  at  full  speed, 
and  the  motor  will  often  continue  to  operate  in  spite  of  poor  con- 
ditions whereas  it  cannot  be  started  again,  once  it  has  become 
cold,  without  first  remedying  the  faults. 

Q.  What  is  the  commonest  cause  of  failure  to  start  a  motor 
equipped  with  low=tension  ignition? 

A.  Dirty  plugs,  or  ignitors,  are  probably  the  most  frequent 
cause.  As  in  the  case  of  the  high-tension  spark  plugs  just  men- 
tioned, the  engine  may  continue  to  run  with  the  plugs  in  poor 
condition,  but  once  it  has  been  shut  down  and  allowed  to  become 
cold,  the  magneto  will  not  produce  a  spark  at  the  dirty  plugs  at 
the  low  speed  at  which  the  engine  is  cranked.  Whenever  an 
engine  with  this  type  of  ignition  is  difficult  to  start,  the  first 
thing  to  do  is  to  examine  the  plugs.  Give  them  a  thorough  clean- 
ing with  gasoline  and  a  wire  brush,  taking  out  the  moving  contact 
to  remove  any  soot  that  has  been  forced  into  the  bearing.  These 
plugs  may  be  tested  by  laying  on  the  cylinder  head,  contacts  up, 
and  snapping  the  contact  with  a  small  piece  of  wood  while  an 
assistant  turns  the  motor  over  so  that  the  magneto  is  generating. 

Q.    What  other  attention  do  these  plugs  require? 

A.  The  contact  points  burn  away  rapidly  and  need  frequent 
dressing  up  to  keep  their  contact  faces  from  becoming  pitted. 
They  should  be  trued  up  in  the  same  manner  as  directed  for  the 
magneto  breaker-box  contact  points,  and  while  the  material  is  not 
so  expensive,  no  more  than  necessary  should  be  taken  off.  The 
operation  should  be  repeated  at  frequent  intervals  to  keep  the 
plugs  in  good  condition. 

Q.  How  may  the  low=tension  magneto  be  tested  to  find 
out  whether  it  is  generating  or  not? 

A.  Place  a  screwdriver  blade  against  the  single  terminal  of 
the  magneto  and  hold  the  end  against  some  metal  part  of  the 


GASOLINE  TRACTORS  161 

motor  while  the  motor  is  cranked.  Move  the  tip  of  the  screw- 
driver over  the  metal  while  maintaining  contact  with  the  terminal 
at  the  other  end  and  sparks  will  be  noted  at  the  tip.  A  similar 
test  may  be  made  by  disconnecting  the  cable  leading  from  the 
coil.  Rub  the  metal  terminal  of  this  cable  over  different  adjacent 
parts  of  the  motor  so  that  contact  is  made  and  broken  while  the 
engine  is  being  cranked,  and  much  larger  sparks  will  be  noted. 

Q.  If,  after  making  tests  successfully,  no  spark  is  obtain= 
able  at  the  ignitor  plug  itself,  what  is  the  cause  of  the  trouble? 

A.  The  plug  is  likely  to  be  at  fault.  Oil  that  has  been  used 
for  any  time  carries  in  solution  a  considerable  percentage  of 
carbon  in.  a  finely  divided  state.  When  hot,  this  oil  is  thin  and 
is  forced  into  the  insulation  of  the  plug,  short-circuiting  it, 
though  apparently  there  is  nothing  wrong  with  it.  The  only 
remedy  is  to  renew  the  insulation  of  the  plug. 

Q.  Though  a  test  of  the  ignitors  shows  them  to  be  in  good 
working  condition,  the  motor  still  fails  to  start  and  examination 
shows  every  other  part  to  be  working  properly,  so  that  the  fault 
is  evidently  with  the  ignition,  what  is  the  cause? 

A.  Either  some  part  of  the  ignitor  tripping  mechanism  has 
failed,  so  that  the  contacts  do  not  separate,  or  the  timing  has 
become  deranged,  so  that  the  separation  takes  place  at  the  wrong 
moment.  In  the  latter  case  the  spark  is  occurring  in  the  cylinder, 
but  it  is  taking  place  either  too  soon  or  too  late  to  fire  the  charge. 
Check  up  the  timing  of  the  ignitor  mechanism  in  accordance  with 
the  maker's  instruction  book. 

Q.  How  can  the  dry  cells  ordinarily  used  for  starting  with 
low=tension  ignition  be  tested? 

A.  A  pocket  ammeter,  or  so-called  battery  tester,  should  be 
used  for  this  purpose.  Hold  the  tips  on  the  cells  only  long  enough 
to  allow  the  instrument  needle  to  come  to  rest,  since  the  ammeter 
represents  a  dead  short-circuit  on  the  battery  and  will  run  it  down 
very  quickly.  If  the  reading  of  the  ammeter  shows  less  than  10 
amperes,  the  batteries  are  of  no  further  use  for  starting  purposes 
and  should  be  renewed.  Any  other  method  of  testing  will  only 
show  whether  the  battery  is  actually  dead  or  not,  and  dry  cells 
may  make  a  fairly  large  spark  through  the  coil  but  will  give  a 
reading  of  only  2  to  3  amperes  on  the  instrument  and  will  fail  to 


162  GASOLINE  TRACTORS 

ignite  the  charge  in  the  cylinder.  Batteries  when  this  low  give 
out  very  quickly.  If  the  switch  has  been  left  on  the  battery  side 
inadvertently,  give  the  cells  ten  to  fifteen  minutes  to  recuperate 
and  then  test  again. 

Q.  What  is  likely  to  go  wrong  with  the  wiring  of  a  low- 
tension  system? 

A.  About  the  only  thing  that  can  happen  to  this  wiring  is  a 
loose  connection  at  the  magneto,  at  the  ground  on  the  motor,  at 
the  ignitor  connection,  or  at  the  switch.  The  switch  itself  may 
become  short-circuited  and  thus  prevent  any  current  from  reach- 
ing the  plugs. 

Q.  Does  the  tripping  mechanism  of  a  low=tensiqn  system 
require  frequent  attention? 

A.  The  trip-rod  mechanism  should  be  inspected  from  time 
to  time  to  see  that  it  is  working  normally,  as  the  vibration  is  likely 
to  knock  it  out  of  adjustment.  The  springs  should  be  replaced 
whenever  they  show  any  signs  of  weakening. 

RUNNING  TROUBLES 

Q.     What  causes  the  engine  to  emit  smoke? 

A.  Among  the  causes  are  the  following:  an  over-rich  mixture 
caused  by  faulty  adjustment  of  the  carburetor;  and  flooding  of  the 
carburetor  due  to  a  leaking  metal  float  or  a  water-logged  cork 
float.  In  either  of  these  cases  the  smoke  will  be  black.  Oil  get- 
ting into  the  combustion  chambers  in  excess,  caused  by  feeding 
too  much  oil  or  by  broken  or  stuck  piston  rings,  will  produce  a 
blue  smoke.  Feeding  an  excessive  amount  of  water  when  burning 
kerosene  or  running  the  engine  too  cold  will  produce  a  white  or 
gray  smoke,  indicating  that  the  kerosene  is  not  being  entirely 
consumed. 

Q.     What  is  the  cause  of  back  firing  through  the  carburetor? 

A.  A  slow-burning  fuel  mixture  is  being  fed,  that  is,  one 
either  too  lean  or  too  rich,  usually  the  former,  so  that  there  is 
still  flame  in  the  cylinder  when  the  valve  opens.  At  times  this 
will  occur  to  such  an  extent  that  the  flame  issues  from  the  exhaust 
pipe  at  the  end  of  the  muffler.  This  is  an  indication  that  the 
mixture  is  too  rich,  since  it  is  still  burning  after  being  exhausted 
from  the  cylinder.  One  of  the  valves  may  not  be  closing  properly; 


GASOLINE   TRACTORS  163 

it  may  be  held  off  its  seat  slightly  by  an  accumulation  of  carbon, 
or  its  stem  may  have  become  bent,  so  that  the  spring  cannot 
close  it.  When  the  ignition  has  been  dismantled,  reassembling 
the  cables  on  the  wrong  plugs  so  as  to  alter  the  firing  order  will 
cause  a  back  fire,  but  in  this  case  the  engine  cannot  be  started. 
An  air  trap  in  the  fuel  line  or  partial  clogging  of  the  latter  will 
also  cause  this  at  times. 

Q.     What  are  the  commoner  causes  of  missing? 

A.  The  most  frequent  cause  is  a  defective  spark  plug. 
Owing  to  the  heat  and  the  vibration  the  porcelain  of  a  plug  will 
break,  but  the  cracks  will  be  so  small  that  they  are  invisible. 
The  pressure  forces  carbon-laden  oil  into  these  cracks  and  the 
plug  becomes  short-circuited,  though  apparently  in  good  order. 
Test  by  short-circuiting  the  plugs  in  turn  with  a  wooden-handled 
screwdriver.  When  short-circuiting  a  plug  causes  no  perceptible 
difference  in  the  running  of  the  engine,  replace  it.  Pitted  and 
badly  worn  contact  points  in  the  magneto  breaker  box  wTill  also 
cause  irregular  running.  (See  the  directions  given  under  Failure 
to  Start.)  Missing  may  also  be  caused  by  the  fuel  mixture  being 
too  rich  or  too  lean,  partial  stoppage  of  the  fuel  line,  water  in  the 
gasoline,  defective  insulation  or  loose  connections,  carbon  dust  on 
the  distributor  plate  of  the  magneto,  or  a  sticking  valve. 

Q.  In  what  other  ways  may  spark  plugs  fail  besides  the 
porcelain  cracking? 

A.  Very  frequently  the  electrodes  burn  too  far  apart,  so  that 
the  current  is  unable  to  jump  the  gap,  or  if  it  does,  the  spark  is 
weak  and  irregular.  Plugs  become  foul  through  an  accumulation 
of  soot  in  them,  and  to  clean  a  badly  sooted  plug  out  thoroughly, 
it  may  be  necessary  to  take  it  apart.  The  insulation  of  a  mica 
plug  will  fail  in  time  through  the  hot  oil  and  carbon  being  driven 
into  it  under  pressure,  and  the  only  remedy  is  to  replace  the 
insulator.  Leakage  around  the  gasket  sometimes  occurs,  and 
when  it  is  not  sufficient  to  cause  a  hissing  noise,  it  will  be  indi- 
cated by  the  porcelain  of  the  plug  becoming  very  dirty.  Squirt  a 
little  oil  on  the  porcelain  when  the  engine  is  running  and  bubbles 
will  form  at  the  gasket  if  the  plug  is  leaking.  Cheap  plugs  are 
made  with  iron  electrodes,  and  the  latter  burn  away  so  fast  that 
it  may  be  necessary  to  adjust  the  gap  once  a  day. 


164  GASOLINE  TRACTORS 

Q.    What  is  the  cause  of  preignition? 

A.  Usually  an  accumulation  of  carbon  in  the  combustion 
chamber.  This  carbon  deposit  often  takes  the  form  of  small 
cones  which  become  incandescent  when  the  engine  is  running 
under  full  load  so  that  the  fresh  mixture  is  ignited  the  moment 
it  enters  the  cylinder.  When  running  on  kerosene,  the  piston 
head  may  become  so  hot  as  to  produce  the  same  result.  In 
either  case,  preignition  will  be  evidenced  by  a  heavy  pounding 
and  the  engine  should  be  stopped  at  once  as  this  imposes  a  very 
heavy  stress  on  all  the  moving  parts.  Increasing  the  amount  of 
water  fed  with  the  fuel  will  remedy  it  when  it  is  due  to  over- 
heated pistons  and  the  use  of  kerosene.  Otherwise,  the  engine 
will  have  to  be  cleaned  out  to  remove  the  carbon. 

Q.     How  can  the  accumulation  of  carbon  be  prevented? 

A.  By  using  only  the  grade  of  oil  recommended  by  the 
manufacturer  of  the  tractor;  cleaning  it  out  and  putting  in  a 
fresh  supply  as  often  as  directed;  keeping  the  piston  rings  in  good 
condition,  so  that  an  excessive  amount  of  oil  cannot  find  its  way 
into  the  combustion  chambers;  and  keeping  the  carburetor 
properly  adjusted,  so  that  too  rich  a  mixture  is  not  used.  Feed 
the  proper  amount  of  water  when  burning  kerosene.  In  spite  of 
these  precautions,  more  or  less  carbon  will  always  accumulate  in 
the  cylinders.  This  amount  can  be  kept  down  to  a  minimum  by 
pouring  a  few  ounces  of  kerosene  into  each  cylinder  at  the  end  of 
a  day's  run  when  the  engine  is  still  very  hot  and  leaving  this  in 
the  cylinders  over  night.  Before  starting  up  in  the  morning,  the 
compression  seal  should  be  renewed  by  putting  a  few  ounces  of 
fresh  oil  into  each  cylinder. 

Q.  When  the  engine  fires  regularly  but  the  explosions  are 
so  weak  that  very  little  power  is  produced,  what  is  the  cause  of  the 
trouble? 

A.  Some  of  the  commoner  causes  are  as  follows:  spark  plug 
points  burned  too  far  apart;  excessive  clearance  at  the  valve  stem 
tappets  or  rocker  arms,  so  that  only  a  fraction  of  the  fuel  required 
is  being  admitted;  valves  in  need  of  grinding;  poor  compression 
caused  by  oil  not  being  renewed  at  sufficiently  short  intervals; 
broken  or  stuck  piston  rings;  leaks  around  spark  plugs;  use  of  a 
fuel  mixture  that  is  too  lean  or  too  rich,  so  that  slow  burning 


GASOLINE  TRACTORS  165 

results  instead  of  an  explosion;  a  weakened  or  broken  valve 
spring;  clogging  of  the  passages  of  the  muffler  with  carbon;  or 
any  obstruction  in  the  exhaust  piping. 

Q.  What  causes  the  engine  to  run  regularly  for  a  time 
and  then  to  misfire  badly? 

A.  This  may  be  caused  by  switching  to  kerosene  before  the 
engine  has  run  long  enough  on  gasoline  to  become  thoroughly 
warmed  up;  a  valve  with  a  bent  stem  that  operates  properly  at 
times  and  then  sticks  during  a  few  revolutions;  air  leaks  around 
the  valve  stems  or  in  the  intake  manifold;  dirt  in  the  carburetor, 
so  that  the  nozzle  is  partly  clogged  at  times  and  free  at  others; 
defective  insulation  or  a  loose  connection  which  interrupts  the 
circuit  from  time  to  time  owing  to  the  vibration  of  the  engine, 
causing  it  to  change  position ;  water  in  the  gasoline ;  carbon  on  the 
distributor  plate  of  the  magneto;  or  faulty  spark  plugs  which  will 
permit  the  engine  to  run  regularly  when  idling  but  which  will  fail 
the  moment  the  load  is  applied.  A  spark  plug  with  fine  cracks  in 
the  porcelain  will  fail  under  load  owing  to  the  greatly  increased 
pressure  in  the  cylinder,  but  will  often  spark  regularly  when  the 
engine  is  running  without  load.  A  loose  connection  or  weak  spot 
in  the  insulation  is  the  most  puzzling  of  these  causes  since  it  is 
often  the  most  difficult  to  find. 

Q.    What  causes  the  engine  to  stop  suddenly? 

A.  This  is  generally  due  to  a  failure  of  the  ignition,  owing 
to  a  break  in  the  circuit  caused  by  a  connection  dropping  off,  the 
switch  suddenly  opening  under  the  vibration,  or  some  part  of  the 
wiring  becoming  short-circuited.  Clogging  of  the  fuel  line  or  of 
the  carburetor  nozzle  or  an  empty  tank  will  also  result  in  the 
engine  stopping.  Where  the  stoppage  is  due  to  failure  of  the  fuel 
supply  from  any  cause,  the  engine  will  not  usually  come  to  as 
sudden  a  stop  as  when  the  ignition  fails.  The  contacts  in  the 
breaker  box  of  the  magneto  may  have  stuck  together.  If  the 
cooling  or  the  lubricating  system  fails,  it  will  also  take  more  time 
to  bring  the  engine  to  a  stop  and  there  will  be  noises  that  give 
ample  evidence  of  the  cause  of  the  trouble.  The  engine  should  be 
shut  off  the  moment  these  noises  occur  for  otherwise  it  will  be 
forcibly  stopped  by  the  binding  of  the  pistons,  thus  putting  the 
engine  out  of  commission. 


166  GASOLINE   TRACTORS 

ENGINE   NOISES 

Q.  How  are  the  different  engine  noises  that' signify  trouble 
in  the  operation  of  the  motor  characterized? 

A.  Experienced  motor  mechanics  give  a  different  term  to 
each  one  of  several  distinct  classes  of  noise  indicating  faulty 
operation,  such  as  knock,  hammer,  pound,  and  slap,  and  to  the 
ear  that  is  familiar  with  them  each  can  be  distinguished. 

Q.  What  do  these  different  noises  signify  to  the  experi= 
enced  ear? 

A.  A  knock  is  the  first  indication  of  looseness  in  a  bearing, 
usually  a  connecting-rod  big  end,  and  the  sound  is  generally  that 
of  a  sharp  metallic  blow.  When  it  is  allowed  to  develop  or  when 
looseness  in  the  crankshaft  bearings  develops,  the  sound  becomes 
louder  but  not  so  sharp  and  is  more  aptly  described  as  hammer- 
ing, owing  to  its  similarity  to  the  blow  of  a  sledge.  Pounding  is 
caused  by  preignition  and  by  overheating  and  is  so  violent  as  to 
rack  the  whole  motor  very  badly.  Slap  is  the  result  of  worn 
pistons,  the  skirts  or  lower  ends  of  which  are  banged  against 
the  cylinder  walls  every  time  the  motor  fires.  The  noise  pro- 
duced is  very  similar  to  that  of  a  knock  and  is  often  mistaken 
for  the  latter,  though  an  experienced  mechanic  will  seldom  go 
wrong  on  this.  In  addition  to  the  noises  mentioned,  there  is 
another  that  is  readily  distinguished  by  the  experienced  ear,  and 
that  is  the  clatter  caused  by  a  loose  valve  motion,  indicating 
that  an  excessive  amount  of  clearance  has  been  allowed  to  develop 
between  the  valve  tappets  and  stems  or  in  the  rocker  arms.  To 
the  inexperienced  ear  all  strange  noises  will  be  knocks  and  it  may 
seem  to  be  drawing  too  fine  distincti6ns  to  differentiate  between 
knocking,  hammering,  and  pounding,  but  familiarity  with  a  motor 
will  enable  the  operator  not  only  to  make  these  distinctions  but 
to  know  as  well  what  causes  the  different  noises. 

Q.  Which  of  these  noises  calls  for  immediate  attention  on 
the  part  of  the  operator  to  prevent  damage  to  the  motor? 

A.  A  very  good  rule  to  follow  is  to  shut  the  motor  down 
the  moment  any  of  these  noises  is  heard  and  correct  the  trouble, 
but  those  that  call  for  immediate  attention  to  prevent  serious 
damage  are  hammering  and  pounding.  The  first  indicates  a  very 
loose  bearing,  which  may  result  in  a  broken  crankshaft  if  allowed 


GASOLINE  TRACTORS  167 

to  run  a  moment  longer  than  necessary,  while  pounding  not  only 
imposes  exceedingly  heavy  stresses  on  every  part  of  the  motor 
but  may  also  be  the  first  sign  of  failure  of  either  the  cooling  or 
the  lubricating  system.  The  cause  may  be  nothing  more  serious 
than  lack  of  sufficient  water  when  burning  kerosene  or  the  fact 
that  the  spark  lever  may  be  advanced  too  far. 

GOVERNOR 

Q.  What  causes  the  engine  to  race  when  the  load  is  thrown 
off? 

A.  The  governor  needs  adjustment,  or  the  connection  between 
it  and  the  throttle  has  parted. 

Q.    What  attention  does  the  governor  ordinarily  need? 

A.  This  depends  largely  upon  the  type  of  governor.  Some 
are  housed  in  and  the  lubrication  provided  for  by  filling  the 
housing  with  oil;  such  a  governor  needs  very  little  attention, 
except  to  adjust  it  when  it  permits  the  engine  to  idle  too  fast. 
An  adjusting  screw  is  provided  for  this  purpose.  With  the  engine 
running,  turn  the  screw  gradually  until  the  engine  slows  down 
to  a  point  where  it  idles  satisfactorily.  The  governor  spring 
weakens  in  time,  and  the  adjustment  is  provided  to  permit  of 
increasing  the  tension.  Apart  from  this,  the  only  regular  atten- 
tion required  by  those  types  which  are  not  automatically  lubri- 
cated is  to  oil  the  bearings  at  regular  intervals  and  see  that  the 
connecting  linkage  is  in  good  order. 

CLUTCH   AND   TRANSMISSION 

Q.     What  provision  is  made  for  taking  up  wear  in  the  clutch? 

A.  The  friction  surface,  which  is  usually  asbestos  on  a  wire 
foundation,  should  be  replaced  when  worn  sufficiently  to  require 
it.  After  considerable  service  the  spring  pressure  may  let  up 
sufficiently  to  cause  unsatisfactory  operation  of  the  clutch.  An 
adjustment  is  provided  for  increasing  the  tension  of  the  spring, 
and  this  should  be  tightened  just  enough  to  make  the  clutch  hold 
under  load;  but  it  is  not  good  practice  to  attempt  to  make  up  for 
a  badly  worn  friction  facing  by  increasing  the  tension  of  the 
spring.  Replace  the  facing  first.  This,  of  course,  does  not  apply 
to  the  type  employing  metal  to  metal  contact  surfaces.  Apart 


168  GASOLINE   TRACTORS 


from  this,  the  chief  attention  required  is  lubrication,  which  should 
be  carried  out  in  accordance  with  the  manufacturer's  instructions, 
some  clutch  mechanisms  calling  for  oil  as  much  as  two  or  three 
times  a  day. 

Q.  Is  it  good  practice  to  let  the  machine  stand  with  the 
clutch  out  of  engagement? 

A.  No;  as  it  only  weakens  the  clutch  spring  and  shortens 
its  life.  Whenever  the  machine  is  to  stand  more  than  a  few 
moments,  the  gears  should  be  shifted  to  neutral  and  the  clutch 
allowed  to  engage.  It  is  particularly  bad  practice  to  let  the 
machine  stand  over  night  with  the  clutch  out  of  engagement. 

Q.  Are  a  worn  friction  facing  and  a  weak  spring  the  only 
causes  of  a  slipping  clutch? 

A.  Allowing  oil  or  grease  to  fall  on  the  friction  faces  of  the 
clutch  will  cause  it  to  slip  badly. 

Q.    What  attention  does  the  transmission  require? 

A.  Maintain  the  oil  level  as  indicated  in  the  manufacturer's 
instructions  and  use  only  the  oil  called  for  by  the  latter.  Drain 
as  often  as  instructed,  and  wash  out  with  gasoline  or  kerosene 
before  refilling.  This  is  usually  two  to  three  times  a  season, 
though  some  types  may  require  it  oftener.  When  the  case  has 
been  cleaned  out,  inspect  the  gear  teeth  carefully  for  breaks, 
and  see  that  any  chips  or  foreign  matter  are  removed.  By 
filtering  the  old  oil  through  several  thicknesses  of  cloth,  it  may 
be  used  for  other  farm  machines  which  do  not  require  the  same 
high  degree  of  lubrication  as  the  tractor. 

Q.     Does  the  differential  require  any  special  form  of  attention? 

A.  The  differential  is  frequently  combined  with  the  trans- 
mission, so  that  it  is  lubricated  by  the  same  supply  of  oil.  Where 
it  is  separate  from  the  transmission,  the  attention  required  is  the 
same  as  that  just  mentioned  for  the  transmission. 

HOUSING  TRACTOR 

Q.     Does  it  pay  to  build  a  special  shelter  for  a  tractor? 

A.  It  will  undoubtedly  be  found  a  good  investment,  since 
the  cost  of  a  building  large  enough'  to  shelter  the  tractor  and 
provide  a  working  bench  beside  it  will  usually  be  less  than  the 
added  depreciation  incurred  by  leaving  it  exposed  to  the  weather. 


GASOLINE  TRACTORS  169 

*Q.  When  the  tractor  is  put  up  for  the  season,  what  atten= 
tion  should  be  given  it? 

A.  Before  putting  the  machine  away  for  the  winter,  the'  valves 
should  be  ground,  the  bearings  adjusted,  the  valve  mechanism 
and  the  magneto  overhauled,  the  oil  drained  from  the  crankcase 
and  the  transmission,  and  the  latter  washed  out  and  provided 
with  a  fresh  supply  of  oil.  Wash  the  cylinders  and  pistons  by 
putting  a  pint  or  more  of  gasoline  in  each  cylinder  and  running 
the  motor  for  half  a  minute.  Then  put  a  pint  of  fresh  oil  in 
each  cylinder  and  turn  the  motor  over  by  hand  a  few  times  to 
spread  it  over  the  surfaces;  otherwise,  the  cylinders  and  pistons 
may  rust.  Coat  all  exposed  parts  with  grease  and  cover  the 
machine  with  a  tarpaulin  or  old  canvas.  Make  a  list  of  all 
replacement  parts  necessary  and  order  them  at  the  time  the 
machine  is  put  away  in  order  that  they  may  be  installed  during 
the  winter. 


INDEX 

A 

PAGE 

Air,  need  for  cleaning 41 

Air  cleaners 43 

air-washer  type : . . . .  43 

attention  required 45 

centrifugal  type 43 

felt  baffle  type 45 

Air  conditions  in  tractor 41 

Air  and  gasoline  supply 29,  30,  37 

Air  washer 43 

Amperage  and  voltage 66 

Automobile  and  tractor 1,  60,  111,  126 

Avery  horizontal-opposed  engine 90 

B 

Bearings 134 

Bevel  friction  drive 109 

Bosch  impulse  starter 84 

C 

Camshaft  and  timing  gear 19 

Carburetor 145 

Centrifugal  air  cleaner 43 

Centrifugal  governors 97 

auxiliary  types 99 

built-in  types 102 

Circuit 64 

Clutch 103 

Clutch  troubles  and  remedies 167 

Condenser 70 

Conductors 63 

Cone  clutch 108 

Contact  breaker 78 

Contracting-band  clutch 108 

Control  in  gasoline  tractors 97 

clutches 103 

engine  governors : 97 

transmissions Ill 

Control  system  lubrication 133 

Cooling  circulation,  types  of 57 

Cooling  systems  in  gasoline  tractors 56,  149 

Current 62 

D 

Distillates  of  petroleum 27 


2  INDEX 

E 

PAGE 

Eagle  horizontal  engine 90 

Eisemann  impulse  starter 86 

Electrical  principles 62 

circuits 64 

conductors 63 

electric  current 62 

electrical  units 63 

low-  and  high-tension 67 

voltage  and  amperage 66 

Electrical  units 63 

Engine 9,  153 

failure  to  sta/t 153 

Engine  parts 10,  14,  134 

details  of  operation 134 

engine  bearings 134 

pistons 142 

valves 137 

Engine  troubles 153 

clutch  and  transmission 167 

engine  noises 166 

failure  to  start : 153 

governor 167 

housing  tractor 168 

running  troubles 162 

Engine  types 87 

Expanding-shoe  clutch 107 

Explosion  motors 25 

F 

Failure  to  start  engine 153 

Felt  baffle  air  washer 45 

Final-drive  group 123 

Firing  order 80 

Force-feed  splash  lubrication 52 

Forced  cooling  circulation 58 

Four-cycle  motor 9 

Four-cycle  principle 10 

compression  stroke 11 

exhaust  stroke 12 

intake  stroke 10 

power  stroke 1 '- 

Fresh-oil  lubrication 55 

Friction  drive 109 

bevel  friction  drive 109 

Fuel 

products  of  distillation 

vaporizing 128 


INDEX  3 

PAGE 

Fuel  supply  system 16,  25 

air  and  fuel  balanced ? 37 

details  of  spraying  process 31 

effect  of  increasing  speed 32 

fuels  available 26 

gasoline  and  kerosene  carburetor 39 

heating  requirements 34 

need  for  cleaning  air 41 

operating  principle  of  internal-combustion  motor 25 

proportion  of  air  to  gas 30 

tractor  air  conditions  very  bad 41 

types  of  air  cleaners 43 

vaporizing  fuel 28 

G 

Gas  and  air  in  carburetion 29,  30,  37 

Gasoline  heating  requirements  in  carburetion 34 

Gasoline  and  kerosene  carburetor 39 

Gasoline  tractors 1-169 

analysis  of  tractor  mechanisms 9 

control  system 97 

motors 9 

introduction 1 

operation 125 

Governor 97 

Governor  troubles 167 

H 

Heat  efficiency  of  motors 56 

Heating  requirements  in  carburetion 34 

gasoline 34 

kerosene 35 

High-tension  ignition  system 69 

High-tension  magneto 76 

High-tension  magneto  circuit 77 

Horizontal  engine 89 

Eagle 90 

horizontal-opposed  Avery 90 

Oil-Pull 89 

Horsepower  ratings 152 

Housing  tractor 168 

I 

Ignition  system 16,  61 

electrical  principles 62 

importance  of 61 

types  of  ignition  systems 68 

Impulse  starter 84 

Bosch 85 

Eisemann .  ,  86 


4  INDEX 

PAGE 

Induction  coil 69 

Internal-combustion  motor,  principle  of 25 

Internal-combustion  vs.  steam  tractors 9 

K 

Kerosene  and  gasoline  carburetor •>. 39 

Kerosene  heating  requirements  in  carburction 35 

L 

L-head  motor,  valves  in 18 

Low-tension  currents 67 

Low-tension  ignition 68,  73 

spark  coil 68 

timing  of 73 

Low-tension  magneto 72 

Lubrication  in  gasoline  tractors 45,  129 

M 

Magneto 72,  76 

high-tension 76,  81 

low-tension 72 

Magneto  impulse  starter 84 

Make-and-break-circuit  mechanisms 70 

Modified  splash  lubrication 49 

Moline  vertical  tractor  motor 94 

Motor 9,  153 

Motor  governor 97,  107 

Motor  lubrication  of  gasoline  tractors 129 

Motor  parts 10,  14,  134 

Motor  troubles 153 

Motor  types 87 

horizontal  engine 89 

vertical  motors 93 

wide  range 87 

O 
Oil,  necessity  for  discarding  when  used 52 

P 

Parrett  vertical  motor 94 

Piping  and  connections  for  fuel  supply  in  gasoline  tractors 142 

Plate  clutch 106 

Pressure-circulated  lubrication 54 

Pressure  and  temperature  in  explosion  motor 12,  45 

R 

Radiator,  protection  of  from  stresses 59 

Rating  motors 152 

Running  troubles 162 


INDEX  5 

S 

PAGE 

Sixteen-valve  engine 24 

Twin  City  multiple-valve  engine 25 

Spark  coil 68 

Spark  gap 71 

Spark  plugs 81 

Splash  lubrication 48 

Spraying  process  in  carburetion 28,  31 

Steam  vs.  internal-combustion  tractors 9 

T 

Temperature  and  pressure  in  explosion  motor 12,  45 

Thermosiphon  circulation 58 

Timing  gear : 19 

Timing  valves '. 21 

Tracklayer  vertical  motor 93 

Tractor  (see  Gasoline  tractor) 1 

Tractor  air  conditions  very  bad 41 

Tractor  and  automobile 1,  60,  111,  126 

Tractor  classes 2 

development  of  tractor  industry 2 

lack  of  standardization 2 

types  of  tractors 3 

Tractor  clutches 103 

functions 103 

friction  drive 109 

types 104 

Tractor  fuel  supply  system 16,  25 

Tractor  ignition  system 16,  61 

Tractor  industry 2 

Tractor  lubrication 129 

control  system 133 

motor 129 

Tractor  mechanisms 9 

control  system 97 

motors 9 

Tractor  motor  troubles 153 

Tractor  motors 9 

cooling  system 56 

fuel  supply  system 25 

ignition  system 61 

lubrication  system 45 

types  of  motors 87 

valves  and  valve  timing 18 

Tractor  operation 125 

carburetor 145 

cooling  system 149 

engine  parts 134 

engine  troubles 153 


6  INDEX 

PAGE 

Tractor  operation  (continued) 

general  instructions 125 

horsepower  ratings 152 

lubrication 129 

Tractor  parts  giving  most  trouble 126 

spares  necessary 127 

Tractor  selection 4 

financial  return 4 

size  of  farm 5 

size  of  tractor 6 

work  done  on  demonstration  no  criterion 4 

Tractor  size 6 

factors  governing  capacity 8 

margin  of  safety 7 

power  for  belt  work 7 

Tractor  transmissions Ill 

final  drive 123 

function 112 

heavy  types 116 

intermediate  types 117 

range  of  types 112 

special  types 119 

speed  vs.  weight Ill 

speeds 113 

Tractor  types 3 

Transmission Ill,  167 

Twin  City  multiple-valve  engine 25 

V 

Valve  movement,  lead  and  lag  of 22 

Valve  timing 18,  22 

Valves 137 

Valves  and  valve  timing 18 

camshaft  and  timing  gear 19 

lead  and  lag  of  valve  movement 22 

need  of  closely  checking  valves 24 

placing  of  valves 

sixteen- valve  engine 24 

timing  valves 21 

valve  details 18 

Vaporizing  fuel 

mixing  gas  and  air 29 

spraying  necessary 

Vertical  motors 93 

Holt  and  Tracklayer 93 

Moline 94 

Parrett 

Voltage  and  amperage 66 


